Calcium bioavailability and kinetics of calcium ascorbate and calcium acetate in rats

The objective was to investigate the bioavailability and mechanism of calcium absorption of calcium ascorbate (ASC) and calcium acetate (AC). A series of studies was performed in adult Sprague-Dawley male rats. In the first study, each group of rats (n = 10/group) was assigned to one of the five test meals labeled with (45)Ca: (i) 25 mg calcium as heated ASC or (ii) unheated ASC, (iii) 25 mg calcium as unheated AC, (iv) 3.6 mg Ca as unheated ASC, or (v) unheated AC. Femur uptake indicated better calcium bioavailability from ASC than AC at both calcium loads. A 5-min heat treatment partly reduced bioavailability of ASC. Kinetic studies were performed to further investigate the mechanism of superior calcium bioavailability from ASC. Two groups of rats (n = 10/group) received oral doses of 25 mg Ca as ASC or AC. Each dose contained 20 micro Ci (45)Ca. Two additional groups of rats (n = 10/group) received an intravenous injection (iv) of 10 micro Ci (45)Ca after receiving an unlabeled oral dose of 25 mg calcium as ASC or AC. Sequential blood samples were collected over 48 hrs. Urine and fecal samples were collected every 12 hrs for 48 hrs and were analyzed for total calcium and (45)Ca content. Total calcium and (45)Ca from serum, urine, and feces were fitted by a compartment kinetics model with saturable and nonsaturable absorption pathways by WinSAAM (Windows-based Simulation Analysis and Modeling). The difference in calcium bioavailability between the two salts was due to differences in saturable rather than passive intestinal absorption and not to endogenous secretion or calcium deposition rate. The higher bioavailability of calcium ascorbate was due to a longer transit time in the small intestine compared with ASC.     

Increased calcium bioavailability in mice fed genetically engineered plants lacking calcium oxalate

Bioavailable calcium affects bone formation and calcification. Here we investigate how a single gene mutation altering calcium partitioning in the model forage crop Medicago truncatula affects calcium bioavailability. Previously, the cod5 M. truncatula mutant was identified which contains identical calcium concentrations to wild-type, but contains no oxalate crystals. In this study, equal number of male and female mice were randomly grouped and then fed one of four ⁴⁵Ca-containing diets: M. truncatula extrinsically or intrinsically labeled, and cod5 extrinsically or intrinsically labeled. Absorption of the tracer was determined in the legs one day after consumption. The absorption was similar in the M. truncatula and cod5 extrinsically labeled diets; however, in the intrinsically labeled diets, calcium absorption was 22.87% (P < 0.001) higher in mice fed cod5. Our study presents the first genetic evidence demonstrating the nutritional impact of removing oxalate crystals from foods.     

益生元与肠道微生态

益生元是一种非消化的成分,通过选择性的刺激肠道中一种或少数种益生菌的增长和/或活性而对宿主有利.具有抵抗致病菌侵入的天然功能.目前广泛研究的有果糖和半乳糖,体内与体外试验均表明不被正常人酶类所消化,在大肠中容易发酵,粪便内未能检出这种糖的成分.通过大肠细菌对益生元的发酵产生的短链脂肪酸是刺激双歧杆菌和乳杆菌增长的重要因素.应用现代技术获得了人肠道微生物细菌群的组成与种类的多样性.本文综述有关益生元的研究状况,强调益生元选择性刺激的机制和对人生理功能的影响.     

Prebiotics in foods

A wealth of information has been gathered over the past 15 years on prebiotics through experimental, animal and human studies, with the aim to understand the mechanism of actions and elucidate their beneficial health effects to the human host. Significant amount of evidence exists for their ability to increase the bioavailability of minerals and stimulate the immune system, although there is less clear evidence so far for their prophylactic or therapeutic role in gastrointestinal infections. Moreover, the effect of the food delivery vehicle on the efficacy of prebiotics is an area that has been hardly investigated. Besides their beneficial effects, prebiotics influence the textural and organoleptic properties of the food products, such as dairy and baked products. To do this however, they need to be stable during food processing, in particular under conditions of high temperature and low pH.     

Prebiotics and lipid metabolism.

Prebiotics are defined as nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth or the activity of one or a limited number of bacteria (bifidobacteria, lactobacilli) in the colon. Dietary fructans are nutritionally interesting oligosaccharides that strictly conform to the definition of prebiotics and (in view of experimental studies in animals and of less numerous studies in humans) exhibit interesting serum or hepatic lipid lowering properties. Other nondigestible/fermentable nutrients, which also modulate intestinal flora activity, exhibit cholesterol or triglyceride lowering effects. Are changes in intestinal bacterial flora composition or fermentation activity responsible for those effects? What is the future of prebiotics in the nutritional control of lipidaemia and cardiovascular disease risk in humans? Those questions only receive partial response in the present review because studies of the systemic effects of prebiotics are still in their infancy, and require fundamental research devoted to elucidating the biochemical and physiological events that allow prebiotics to exert systemic effects on lipid metabolism.     

益生元-双歧杆菌生长促进因子

微生态学的观点认为肠道菌群的状况与人体健康密切相关,肠道中的有益菌如双歧杆菌、乳酸菌等在净化肠道、改善机体营养和维护宿主健康方面起到重要作用。益生元为人体不消化或难消化的食物成份,其中多数是非消化性的低聚糖,其作用可选择性地刺激肠道有益菌的生长和代谢活性,改善肠道菌群平衡从而有利于人体健康。本文对一些重要的功能性低聚糖的性质、生理功能及其生产了概述。     

Effect of chitooligosaccharides on calcium bioavailability and bone strength in ovariectomized rats

Chitosan polymer with deacetylation degree of 93% was hydrolyzed with an endo-type chitosanase (35,000 U/g protein) with substrate to enzyme ratio of 1 to 1.5 for 18 h in a batch reactor, and then the resultant hydrolysates were fractionated into four different molecular weights using an ultrafiltration (UF) membrane reactor system. An in vitro study elucidated that four kinds of chitooligosaccharides (COSs) could efficiently inhibit the formation of insoluble calcium salts in the neutral pH. In vivo effects of COSs on Ca bioavailability were further studied in the osteoporosis modeling rats induced by ovariectomy and concurrent low calcium intake. During the experimental period corresponding to the menopause with the osteoporosis disease, calcium retention was increased and bone turnover was decreased by COS IV supplementation in the ovariectomized (OVX) rats. After the low Ca diet, COS IV diet including both normal level of calcium and vitamin D significantly decreased calcium loss in feces and increased calcium retention compared to the control diet. The levels of femoral total calcium, bone mineral density (BMD), and femoral strength were also significantly increased by the COS IV diet in a similar level to those of CPP diet group. In the present study, the results proved the beneficial effects of low molecular chitooligosaccharide (COS IV) in preventing negative mineral balance.     

钙对土壤镉有效性的影响及其机理

采用盆栽试验,研究了赤红壤上两种镉污染水平下,施用4种钙量（0、40、100、200 mg·kg^-1）对小油菜生物量、镉吸收量及土壤溶液中钙、镉浓度的影响.结果表明：在低镉或者高镉污染水平下,与对照相比,小油菜干质量均以高钙用量处理的增幅最大,两季平均增加了5.5%（低镉）和17.3%（高镉）;增加钙的施用量,使土壤溶液中钙浓度明显增加,小油菜体内钙浓度也明显增加;当钙施用量为100 mg·kg^-1时,土壤溶液中镉浓度较对照分别增加74.5%（低镉）和31.0%（高镉）,而小油菜体内镉浓度较对照分别降低4.5％（低镉）和13.1％（高镉）.两种镉污染水平下,土壤溶液中钙/镉（质量比）值与小油菜体内镉浓度均呈显著正相关.土壤溶液中钙/镉比值影响土壤镉的有效性,进而影响小油菜对镉的吸收.     

Influence of dietary factors on calcium bioavailability: a brief review

There are several factors that affected calcium bioavailability, such as physiological and dietary factors. These dietary factors help to achieve an appropiate status of calcium for a correct bone mineralization. In this pathway, recently some compounds present in milk that seem improve calcium absorption such as lactose and certain caseinophosphopeptides formed during digestion of caseins have been studied. On the other hand, the possible inhibitatory effect of fiber has been also studied, without conclusive results between in vitro and in vivo studies and the role of phytic acid on impairs calcium bioavailability could be prevented by using fructo-oligosaccharides, which cannot be digested in the small intestine and arrive practically intact to the colon, where are fermented. Finally, calcium fortification must be executed by suitable compounds with high bioavailability, better technological properties, and a correct calcium: phosphorus ratio. For that reason, the objective of the present article is to review the influence of all these conditional factors on calcium bioavailability.     

Prebiotics: why definitions matter

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The rate and extent of calcium bioavailability from two oral dosage forms in rats

The purpose of the present work was to compare oral bioavailability of calcium from two calcium preparations, Calcium Sandoz forte 500 mg and Calcium Spofa effervescens. The pharmacokinetic study was carried out on rats, and plasma levels of 45Ca after administration of labelled calcium solutions were determined. Appropriate equations describing the two-compartment open model and the one-compartment model with first order absorption were fitted to the observed i.v. and oral data, respectively, using weighted nonlinear least-squares regression analysis. The extent and the time profile of the rate of 45Ca systemic bioavailability were assessed. Both parameters suggested identical bioavailability of calcium from the two dosage forms compared.     

Prebiotics and synbiotics: towards the next generation

Recent research in the area of prebiotic oligosaccharides and synbiotic combinations with probiotics is leading towards a more targeted development of functional food ingredients. Improved molecular techniques for analysis of the gut microflora, new manufacturing biotechnologies, and increased understanding of the metabolism of oligosaccharides by probiotics are facilitating development. Such developments are leading us to the time when we will be able to rationally develop prebiotics and synbiotics for specific functional properties and health outcomes.     

Prebiotics and other microbial substrates for gut functionality

The intestinal microbiota is of great importance to our health and wellbeing. Modulation of the intestinal microbiota by exogenous and endogenous substrates can be expected to improve various physiological functions of our body, not just those in the intestine. Recently, new targets such as immune function and areas outside the colon have been considered to be influenced by the intestinal microbiota. Novel approaches might include the application of prebiotics in different combinations or the provision of nutrients to different bacterial groups and to different parts of the intestine.     

Prebiotics: tools to manipulate the gut microbiome and metabolome

Journal of Industrial Microbiology & Biotechnology - The human gut is an ecosystem comprising trillions of microbes interacting with the host. The composition of the microbiota and their...     

The effect of fructooligosaccharides with various degrees of polymerization on calcium bioavailability in the growing rat

Maximizing peak bone mass during adolescence may be the key to postponing and perhaps preventing bone fractures due to osteoporosis in later life. One mechanism to maximize peak bone mass is to maximize calcium absorption, and it has been suggested that inulin and oligofructose might be one of the ways of doing so. In this study, fructooligosaccharides with various degrees of polymerization have been compared in terms of impact on calcium absorption, bone density, and excretion of collagen cross-links in the young adult male rat. The various oligosaccharides were oligofructose (DP2-8), inulin (DP>23), and a mixture of 92% inulin and 8% short-chain oligofructose (DP2-8). Measuring ex vivo bone mineral density (BMD) and bone mineral content (BMC) showed that BMD was significantly higher in the group fed inulin (DP>23) in both femurs, whereas BMC was significantly higher in the spine. The excretion of fragments of Type 1 collagen decreased in all groups over the 4 weeks of feeding, but the decrease was most significant in the group fed inulin (DP>23). Several hypotheses have been offered to explain the effect of the fructooligosaccharides on calcium absorption and retention. These include the production of organic acids that would acidify the luminal contents and enhance solubility and hence absorption, or possibly a mechanism via calbindinD9k. This study is unique in that it compares the different fructooligosaccharides in the same model, and it clearly shows that the various fructans do not have the same effect. In our model, inulin (DP>23) had the most significant effect on calcium bioavailability.     

Selenium metabolism and bioavailability

Selenium (Se) is at once an essential and toxic nutrient that occurs in both inorganic and organic forms. The biological functions of Se are mediated through at least 13 selenoproteins that contain Se as selenocysteine (Se-cyst). The endogenous synthesis of this amino acid from inorganic Se (selenide Se⁻²) and serine is encoded by a stop codon UGA in mRNA and involves a unique tRNA. Selenium can also substitute for sulfur in methionine to form an analog, selenomethionine (Se-meth), which is the main form of Se found in food. Animals cannot synthesize Se-meth or distinguish it from methionine and as a result it is nonspecifically incorporated into a wide range of Se-containing proteins. The metabolic fate of Se varies according to the form ingested and the overall Se status of an individual. This paper reviews the bioavailability, including absorption, transport, metabolism, storage, and excretion, of the different forms of exogenous and endogenous Se.     

Folate bioavailability and health

Since its discovery in 1931 by Lucy Wills, and its first isolation in 1941 by Mitchell, Snell and Williams, our understanding of the fascinating world of folic acid and one-carbon metabolism, and its role in health and disease, has come a long way. However, there is still much to do in perfecting methods to measure folate bioavailability, and status, with a high degree of precision and accuracy. Future examination of the relationships of common gene polymorphims involved in folate bioavailability (folate polyglutamate deconjugation and carrier-mediated absorption) and one-carbon metabolism (methylation cycle, folate cycle and DNA synthesis/repair) to folate status, morbidity, mortality and longevity, need to be considered concurrently rather than as a series of individual associations, as has been the usual practice. This revised version was published online in June 2006 with corrections to the Cover Date.