Hindawi Publishing CorporationGastroenterology Research and PracticeVolume 2012, Article ID 872716, 16 pagesdoi:10.1155/2012/872716

Review ArticleProbiotics, Prebiotics, and Synbiotics: Gut and Beyond

Usha Vyas and Natarajan Ranganathan

Kibow Biotech Inc., Newtown Business Center, 4781 West Chester Pike, Newtown Square, PA 19073, USA

Correspondence should be addressed to Usha Vyas, usha@kibowbiotech.com

Received 16 March 2012; Accepted 20 July 2012

Academic Editor: Maurizio Gabrielli

Copyright 2012 U. Vyas and N. Ranganathan. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

The human intestinal tract has been colonized by thousands of species of bacteria during the coevolution of man and microbes.Gut-bornemicrobes outnumber the total number of body tissue cells by a factor of ten. Recent metagenomic analysis of the humangut microbiota has revealed the presence of some 3.3 million genes, as compared to the mere 23 thousand genes present in thecells of the tissues in the entire human body. Evidence for various beneficial roles of the intestinal microbiota in human health anddisease is expanding rapidly. Perturbation of the intestinal microbiota may lead to chronic diseases such as autoimmune diseases,colon cancers, gastric ulcers, cardiovascular disease, functional bowel diseases, and obesity. Restoration of the gut microbiota maybe dicult to accomplish, but the use of probiotics has led to promising results in a large number of well-designed (clinical)studies. Microbiomics has spurred a dramatic increase in scientific, industrial, and public interest in probiotics and prebioticsas possible agents for gut microbiota management and control. Genomics and bioinformatics tools may allow us to establishmechanistic relationships among gut microbiota, health status, and the eects of drugs in the individual. This will hopefullyprovide perspectives for personalized gut microbiota management.

1. Introduction

Bacteria, unicellular eukaryotes, and other organisms inhabitthe human body in large numbers. The human gut is dom-inated by several bacterial phyla including Bacteroidetes,Firmicutes, and Actinobacteria. The term microbiota, mi-croflora, or normal flora is used to designate this vast hostof microbes which coexist with the host [13].

It is estimated that the human microbiota contains asmany as 1014 bacterial cells, a number that is 10 times greaterthan the number of human cells present in our bodies [46].Virtually every surface of the human body starting from theskin surface to the genitourinary tract, oral cavity, respiratorytract, ear, and the gastrointestinal tract is colonized heavilyby various species of bacteria [3, 79]. By far, the mostheavily colonized organ is the gastrointestinal tract (GIT)which houses a huge microbial ecosystem; the colon aloneis estimated to contain over 70% of all the microbes in thehuman body [4, 6].

The gut microbiota or microflora has a crucial role inhuman health and disease. The GIT is comprised of the entiredigestive system from the stomach to the anus. The colon

or the large intestine is the organ which is the preferredsite for bacterial colonization. The GIT is also rich in manymolecules which can be used as nutrients by microbes.Hence the GIT has the potential to be heavily colonized byvarious bacteria both harmful and beneficial. The mucosaof the gastrointestinal tract is continuously exposed to anenvironment that is rich in foreign substances, such asfood particles and antigens of microbial origin. Particularchanges in the intestinal ecosystem might contribute tothe development of certain illness. There is therefore aneed for an exhaustive review on the functions of thegut microbiota, occurrence of gut dysbiosis (alteration orimbalance of the microflora), how these intestinal bacteriatrigger development of disease once the normal flora of ahealthy individual is imbalanced, exploiting this intricateand interwoven ecosystem for understanding human health,development of biotherapeutics, and future perspectives.

The imbalanced gut bacteria have been studied in diseas-es such as inflammatory bowel disease, antibiotic-associateddiarrhea, colon cancer, hypercholesterolemia, and others.Lactic acid bacteria, belonging to the genus Lactobacillusand Bifidobacterium, have been shown to positively influence

2 Gastroenterology Research and Practice

the microbiota can be viewed as a metabolic organ exquisitely tuned to our

physiology that performs function we have not had to evolve on our own

Backhed et al. 2004. PNAS 101:15718-15723

Amount of bacteria per gram of cellular component

Human body 1013

cells 23,000 genescells on the human body.

3.3 million genes

Nose

Mouth

Smallintestine

Skin

Lungs

Stomach

Colon

RectumUrinary/vaginaltract(s)

14 microbialNormal flora 10

1 to 102 cells Stomach103 cells Duodenum10

4 cells Jejunum104 to 107 cells Ileum 10

10 to 1011 cells Proximal colon 1011 to 1012 cells Transverse colon 10

>1012 cells Distal colon

Nose

Mouth

mallestine

Skin

Lung

Stom

Colon

RectumUrinary/vaginal

Figure 1: The Human Body and number of bacteria present in the total microflora.

health. Hence, re-establishing the balance by using thesebacteria (termed probiotics) for disease treatment and pre-vention should prove advantageous. Probiotics along withprebiotics and synbiotics have been used and studied invarious disease areas. Several studies have indicated that analtered gut microbiota is associated with several diseases thatare particularly prevalent in the 21st century.

N.Williams [10] has previously reviewed the pharmacol-ogy, uses, dosage, safety, drug interactions, and contraindica-tions of probiotics. The first part of this updated and currentreview will give an overview of the gut microbiota andits main characteristics and describe the major factors thatcould modulate gut microbiota composition. The secondpart describes various new diseases and reports on studiesin which probiotics, prebiotics, and synbiotics have beenused. The virtues of probiotics are already well recognizedfor general gut health, antibiotic-associated diarrhea, andimmunity. Application of these areas will not be examined.The last part of the review focuses on future potentialapplications of probiotics, prebiotics and synbiotics in newemerging areas of studies like autism and gut-brain connec-tion. Finally, the paper will conclude with a discussion on thefuture of this field. A short review article of this length cannotdo full justice to this field. A broad overview, composed ofexcerpts taken from various publications including reviewarticles, is presented here. For each of the important areas,we have included references to review articles for readerswishing to delve and analyze more deeply.

2. The GutMicrobiota and Functions

A newborn baby has a sterile gut that is colonized by bacteriafrom the mother and from the babys surroundings or envi-ronment [11]. An adult human has 10 times more bacterial

cells on, and in, the entire body as compared to the totalhuman cells (Figure 1). The human microbiome is highlycomplex and diverse. Its composition and number variesfrom the nose andmouth to the distal colon and rectum. Thecomposition and complexity of the gut microbiota changeswhen the baby is weaned to solid foods. Dietary changes inadulthood are also greatly responsible for the compositionof gut microbiota. Development of 16S ribosomal RNA(rRNA) gene-sequence-based metagenomic methods has ledto major advances in defining the total microbial populationof the gut [12]. This technique has been used to showthat 90% of the bacteria belong to two phyla, namely, theBacteroidetes and Firmicutes [13].

The gut microbiota plays an important role in themaintenance of health. These are summarized below.

2.1. Structure and Histological Function. The intestinal struc-ture and function is ensured by the microbiota presentwithin. The intestinal mucus layer is a balance of mucin se-cretion and degradation. This mucin layer creates an obstacleto proinflammatory compounds and uptake of antigens [14].Evidence indicates that butyrate induces secretion of mucin,antimicrobial peptides, and other factors. This reinforces thedefense barrier in the colon [15].

Secondly, the gut microflora has a role in the develop-ment of cell and tissue. Butyrate, a short chain fatty acidthat is secreted by these colonic microbes, regulates cellgrowth and dierentiation, inhibits transformation of cellgrowth and helps in reverting the cells from a neoplastic toa nonneoplastic phenotype [16]. The development of themicrovasculature of the intestinal villi is dependent on theindigenous microbes. This has been demonstrated in studiesusing germ-free mice and its subsequent colonization by B.thetaiotamicron by Jerey Gordons group [17]. This signifies

Gastroenterology Research and Practice 3

SCFAs

AMPs

BacteroidetesB. fragilis (PSA)

Gm-PGGm-LPS

ImmunocompetenceTolerance

DC tolerization

E. coli

Cellular immunityLymphoid organogenesis

Mucosal immunity

IgA

Lapactivation

inactivation

B. thetaiotaomicron

PeristalsisGlycosylation

Barriermaintenance

Bifidobacterium spp.Clostridium spp.

SCFAmetabolism

Lipidmetabolism

Conjugation oflinoleic acid

Xenobiotics metabolismDrug disposition

GIT surface maturationGIT functional maturation

Normalization ofHPA stress response

B. infantis

Angiogenesis

O. formigenes

Lactobacillus spp.

Oxalateexcretion

Behavior

Nutrition

NFB

Figure 2: The complex web of gut microbiota contributions to host physiology. Dierent gut microflora components can aect many aspectsof normal host development, while the microbiota as a whole often exhibits functional redundancy. Members of the microbiota are shownin gray, with their components or products of their metabolism. Their eects on the host at the cellular or organ level are shown in white.Black ellipses represent the aected host phenotypes. Only some examples of microbial members/components contributing to any givenphenotype are shown. AMP: antimicrobial peptides; DC: dendritic cells; Gm: gram negative; HPA: hypothalamus-pituitary adrenal; Iap:intestinal alkaline phosphatase; PG: peptidoglycan; PSA: polysaccharide A. Extracted from: Phys Rev 2010 Sekirov et al.

the importance of the gut microbes in the development ofthe structure and morphology of the gut (Figure 2).

2.2. Metabolic Functions. The gut bacteria are known toproduce a large number of vitamins like the B group ofvitamins, synthesize amino acids, and carry out biotransfor-mation of the bile. Biotransformation of bile by microbialenzymes is important for the metabolism of glucose andcholesterol [18]. Importantly, the microbiome provides themuch needed biochemical pathways for the fermentation ofnondigestible substrates like fibers and endogenous mucus.Fermentation or metabolism of these nondigestible sub-strates leads to the growth of these microbes and the pro-duction of short chain fatty acids and gases [19]. The majorshort-chain fatty acids produced are acetate, propionate,and butyrate. Other bacterial end products include lactate,ethanol, succinate, formate, valerate, caproate, isobutyrate,2-methyl-butyrate, and isovalerate. Bacterial fermentationtakes place in the cecum and colon, where the short-chainfatty acids are absorbed, stimulating the absorption of saltsand water. These short-chain fatty acids have a protectiveeect on the intestinal epithelium [19]. The colonic bacteriaprefer butyrate as the sole source of energy, and most of it iscompletely metabolized. The principal short chain fatty acid

produced in the colon is acetate, and it serves as a substratefor biosynthesis of cholesterol. Thus the gut microbiotaperforms various metabolic acitivities which are essential forthe hosts metabolism (Figure 2).

2.3. Protective Functions. Many of the commensal organ-isms produce antimicrobial compounds and compete fornutrients and sites of attachment in the gut lining, therebypreventing colonization by pathogens. This helps reduce theproduction of lipopolysaccharides and peptidoglycans whichcan all be detrimental to the host [20]. The development ofthe immune system is also governed by the nature of theindigenous microflora [21]. Germ free animals have fewerdendritic cells, and evidence shows that bacterial systemshave a role to play in development of B cells [22, 23]. Thedevelopment of regulatory T cells, T helper type 1 and 2 cells,and T helper 17 cells is also dependent on the signals given bythe intestinal bacteria [2426]. Short-chain fatty acids, suchas butyrate, have been shown to inhibit NF-kB in patientswith ulcerative colitis thus exerting immunomodulatoryeects [27, 28].

These concepts illustrate a dynamic relationship betweenthe immune system and the microbiota. The intestinalmucosa averts threats by signaling to the innate immune

4 Gastroenterology Research and Practice

system through toll-like receptors. These recognize and bindto specific microbial macromolecules, like lipopolysaccha-ride, flagellin, peptidoglycan, and N-formylated peptides. Inthe intestinal mucosa, the activation of toll-like receptorsinitiates nuclear factor-kB pathways, mitogen-activated pro-tein kinase, and caspase-dependent signaling cascades. Theselead to the production and release of protective peptides,cytokines, chemokines, and phagocytes. The result can be aprotective response to commensal bacteria, an inflammatoryresponse to pathogenic organisms, or a trigger of apoptosis.Therefore, commensal bacteria of the gastrointestinal tractplay active roles in the development and homeostasis of theimmune system, as shown in Figure 2.

3. Dysbiosis andModulating ofthe GutMicrobiota

Normal physiology of the host depends on the signals givenby the intestinal microbes. The intestinal lumen consistingof gastric acid, digestive enzymes, and IgA constitutes thefirst line of defense and is lethal to invading and ingestedpathogenic bacteria. The indigenous microbes degradeintraluminal antigens and inhibit the pathogenic microbesfrom adherence and colonization. They also are necessaryfor the induction of regulatory T cells [29]. Any changesto this microbial ecosystem could cause an imbalance ordysregulation of the microbiota (dysbiosis) often associatedwith various disease states ranging from the most commonIBD [30, 31] and IBS [32] to the more unexpected activationof chronic human immunodeficiency virus (HIV) infection[33] and generation of atopy [3436] (Figure 3).

It is therefore important to reestablish the bacterialhomeostasis whichmay have been disturbed by any or severalfactors. One of the ways to favorably alter the intestinalmicrobiota is through the use of prebiotics, probiotics, andsynbiotics (a combination of both prebiotics and probi-otics given together). These agents can favorably influencemicrobial interactions with the immune system and gutepithelium.

A prebiotic is a selectively fermented ingredient thatresults in specific changes in the composition and/or activityof the gastrointestinal microbiota, thus conferring healthbenefit(s) upon the host. Prebiotics are generally oligomersmade up of 4 to 10 monomeric hexose units.

Probiotics, according to the currently adopted definitionby FAO/WHO [37, 38], are Live microorganisms whichwhen administered in adequate amounts confer a health ben-efit on the host. The International Scientific Associationfor Probiotics and Prebiotics (ISAPP with Glenn Gibson,Todd Klaenhammer, and Mary Ellen Sanders on its board ofdirectors) and the International Probiotic Association (IPA,an association of over 150 probiotic business organizationsmanufacturing and distributing probiotics) are two groupswhich are working with these beneficial microbes.

Synbiotics is a combination of probiotics and prebioticsadministered together.

Common, well-known beneficial bacteria which have along-standing association with health include lactic acid pro-ducing genera such as the Bifidobacteria or Lactobacilli. These

bacteria can be introduced into the gut and/or encouragedto multiply either through ingestion by the individual ofappropriate probiotic strains or through the provision ofprebiotic growth substrates also known as soluble fibers.

That probiotics and prebiotics are becoming increasinglypopular is evidenced by rapidly expanding research supportand an ever widening choice of products. Probiotics and pre-biotics are available commercially in many forms, includingfoods, dietary supplements, and clinical therapeutics withoral or non-oral delivery.

To be a candidate for commercialization, a probioticmust retain its properties during large-scale industrial prepa-ration. Naturally, it should also remain viable and stableduring storage and use. For most applications, the probioticshould be able to survive in the intestinal ecosystem andthe host animal should gain beneficially from its presence.Clearly, the organisms used should be generally regarded assafe-GRAS as per USFDA regulations or well documentedin the literature.

Prebiotics must provide selective stimulation of thegrowth or activity of beneficial native bacteria. Since prebi-otics are non-viable, stability is not a concern, but safe con-sumption levels must be established. A detailed guideline forprobiotics and prebiotics has been published by the WorldGastroenterology Organization [39].

4. Clinical Applications of Various Probiotics,Prebiotics and Synbiotics

4.1. Gut Microbiota and Obesity. The metabolic equilibriumof the host is maintained by the gut microbes [40, 41].One study in adult population with type 2 diabetes [42]has shown that their gut microbiota diers from that ofnon-diabetic adults, and that health may potentially improvewhen the gut microflora is modified by the administration ofprobiotics and prebiotics. In spite of these findings, and therelationship between diabetes and abdominal fat, few studieshave been aimed at finding correlations between the compo-sition of the microbiota and the occurrence of inflammationand metabolic alterations in individuals with obesity [42,43]. A study in patients with diabetes mellitus showed thatthese individuals had a lower number of Faecalibacteriumprausnitzii and an increase in with inflammatory markers[43]. Obesity was found to be associated with large changesin the abundances of dierent bacteria from dierent taxa[44].

The Bifidobacteria population (and most other organ-isms in the group of Firmicutes) is slightly lower inindividuals with obesity than in lean people [45]. A similarfinding was reported in patients with type 2 diabetesmellitus in comparison with nondiabetic patients [46]. Thesefindings suggest that Bifidobacteria may play a part inthe development of obesity and its related comorbidities.When prebiotics like inulin-type fructans were fed to mice,these were used as energy substrates by bacteria [4749]. The number of Bifidobacteria increased significantly,and there was an inverse correlation with the levels oflipopolysaccharide, glucose tolerance and development of fat

Gastroenterology Research and Practice 5

Gut-brain hypothesis1. Autism C. bolteae/clostridia sporesmechanism unknown2. Mood: depression, anxiety

Asthma/atopyHygiene hypothesis:Exagergated innate immune responseUpregulation of regulatory T cellsafter capture of Ags by DCs Clostridia

Hypertension/ischemicheartdisease

Biliary disease Altered enterohepatic circulation of bile

Diet high in red meat and animal fatLow SCFA/butyrateHigh fecal fatsLow vitamin absorption 7 dehydroxylating bacteria:cholic acid deoxycholic acid (cocarcinogen)Low in H2S metabolizing bacteria

Altered xenobiotic/drug metabolism

e.g., paracetamol metabolism: predose urinary p-cresol sulfate leads to postdose urinaryacetaminophen sulfate: acetaminophen glucuronide.Bacterially mediated p-cresol generation and competitiveo-sulfonation of p-cresol reduces the eective systemic capacityto sulfonate acetaminophen.

Peripheral vascular disease

Result of metabolic syndrome-

metabolism

Obesity/metabolic syndrome

Bacteroidetes and Actinobacteria in obeseAltered energy/lipid metabolismHigher relative abundance of glycoside hydrolases,carbohydrate-binding modules,glycosyltransferases, polysaccharide lyases, and carbohydrateesterases in the BacteroidetesTLR mediated

Inflammatory bowel disease

Hygiene hypothesisAltered immune response: TLR signalingLess microbial diversityActivation of specific species e.g., Escherichia

Bifidobacteria, gram

altered lipid deposition/

Colon cancer

+ve organisms

Figure 3: Diseases influenced by gut microbial metabolism. The variety of systemic diseases that are directly influenced by gut microbialmetabolism and its influence on other mammalian pathways, such as the innate immune system, are shown. Specifically highlighted arethe metabolic pathways involved in drug metabolism and obesity that are directly influenced by the gut microbial content. Ags, antigens; C.bolteae, Clostridium bolteae; DCs; dendritic cells; SCFA, short-chain fatty acid; TLR, toll-like receptor. Kinross et al. Genome Medicine 20113:14.

mass [47, 48]. Moreover the prebiotic approach preventedthe overexpression of several host genes that are related toadiposity and inflammation.

Studies have been carried out using probiotics to pro-mote specific changes in the gut microbiota. Angiopoetin-related protein 4 (Angptl4), a lipoprotein lipase inhibitorwhich inhibits the uptake of fatty acids from circulatingtriglyceride-rich lipoproteins in white adipose and muscletissues was found to be increased in mice fed with ahigh fat diet supplemented with L. paracasei [50]. Obeseindividuals when administered with Lactobacillus acidophilusNCFM and Lactobacillus gasseri SBT2055 showed a decrease

in fat mass and the risk of type 2 diabetes mellitus andinsulin resistance [51, 52]. In the active group which con-sumed L. gasseri, abdominal, visceral, and subcutaneous fatareas decreased significantly. Body weight also decreasedsignificantly. In the L. acidophilus NCFM study the insulinsensitivity was preserved, but there was no eect on thesystemic inflammatory response. Clinical trials using pre-biotics like arabinoxylan [5355] and inulin-type fructans[5658] have shown positive results in diabetic, overweight,and obese populations. A review article [59] discusses thetight relationship which exists between mammalian gutcomposition and functions and the host metabolism using

6 Gastroenterology Research and Practice

modern molecular techniques. Gut microbes can aect hostmetabolism and energy storage and thus predisposition toobesity and diabetes.

4.2. Allergy and Atopic Diseases of Children. Atopic diseasesarise from aberrant immune responses to environmentalallergens leading to allergic inflammation [60]. The allergicresponses are mediated by the Th2 cells which produceinterleukins-4, -5, -9, and -13. Genetics play a strong role,and genes-encoding proteins which are involved in thepathogenesis of allergic inflammation have been identified[61, 62]. Atopic dermatitis (AD) a common allergic skindisease is widely prevalent in children from US and WesternEurope [63]. Children suering from AD have highernumber of S. aureus and Clostridium in their colon and lowernumber of Enterococcus, Bifidobacterium, and Bacteroides[64, 65]. With the increasing recognition of the importanceof healthy intestinal microbiota, there has been a substantialeort to assess the potential role of probiotics in theprevention and/or treatment of allergic diseases in humanclinical trials. When Lactobacillus GG was administered tohigh risk infants, there was a 50% reduction in observedatopic eczema [66]. In another study in Finland whenchildren were given a whey formula with L. rhamnosus or B.animalis ssp. lactis for 2months, the skin condition improved[67]. Similar curative results were obtained L. rhamnosus plusL. reuteri preparations [68].

In another study, Lactobacillus fermentum reduced symp-toms of atopic dermatitis in infants with moderate-to-severedisease [69]. Supplementation with L. rhamnosus HN001in pregnant women and their newborn infants substantiallyreduced the cumulative prevalence of eczema in infants [70].A probiotic cocktail of Bifidobacterium bifidum, Bifidobac-terium lactis, and Lactococcus lactis was able to significantlyreduce eczema in high-risk infants for a minimum of 2years provided that the probiotic was administered to theinfant within 3 months of birth [71]. A double blind,randomized, and placebo-controlled intervention in childrenwith atopic dermatitis (AD) using Daniscos probiotic strainBifidobacterium animalis subsp lactis. Bi-07 showed thatthere was a significant reduction in the severity of AD withan improved ration of IFN- and IL-10 [72]. Other studiesalso indicate that the consumption of dietary supplementsor foods containing probiotics can stabilize the intestinalbarrier function and decrease gastrointestinal inflammationin children with AD [73].

4.3. Hepatic Encephalopathy. Hepatic encephalopathy is adreaded liver disease. Minimal encephalopathy is a con-dition of chronic liver disease with no clinical symptomsof brain dysfunction. The exact pathogenesis of hepaticencephalopathy is still unknown, and the basis for it is stillnot completely understood [74]. However it is widely agreedthat gut-derived-nitrogenous substances and, specifically,ammonia derived primarily from enteric bacteria play acentral role. Use of probiotics for MHE has been rationalizedbased on various modes of action like decreasing bacterialurease activity, decreasing intestinal permeability, decreasinginflammation, decreasing uptake of other toxins, and other

modes of action. Use of probiotics has been demonstrated toresult in reduced concentrations of many bacteria [75], par-ticularly gram-negative bacteria which produce urease. Theyhave also been shown to improve intestinal permeability inexperimental human models [76]. A rat model of hepaticfailure has shown that certain bacteria can produce a ligandfor the benzodiazepine receptor that may contribute to theencephalopathy [77]. When patients with minimal hepaticencephalopathy were given Bifidobacterium longum withfructooligosaccharide for 9 weeks, their cognitive functionswere seen to improve [78].

Endotoxemia causes inflammation leading to cirrhosisof the liver. When fecal flora of cirrhosis patients wasanalysed, there was a substantial reduction in the levels ofBifidobacteria [79]. Minimal hepatic encephalopathy (MHE)is a complication of cirrhosis during which accumulationof neurotoxic substances in the bloodstream produces neu-rological manifestations. When MHE patients were given asynbiotic preparation of probiotics and prebiotics, the MHEwas reversed in 50% of the patients, and this eect wasaccompanied by a significant increase in Lactobacilli [80].

A recent review on the role of probiotics for hepaticencephalopathy concludes the need for further random trialsbefore probiotics can be endorsed for hepatic encephalopa-thy [81].

4.4. Hypocholesterolaemic and Cardioprotective Eects. Hy-percholesterolemia, or elevated level of total cholesterol inthe bloodstream, is the result of high levels of low-densitylipoprotein (LDL) as compared to high-density lipoprotein(HDL) cholesterol. Many Lactobacilli, being the naturalinhabitants of the intestine, possess bile-salt hydrolase activ-ity. This property has been used for developing probioticformulations to combat hypercholesterolemia.

Many animal models have been used to evaluate theeects of probiotics and prebiotics on serum cholesterol lev-els in many studies. When Abd El-Gawad used bualo milk-yogurt fortified with B. longum in male albino rats for 35days, total cholesterol was reduced by 50%, LDL-cholesterolby 56%, and triglycerides by 51% in comparison to thecontrol [82]. When L. plantarum PH04 was evaluated for itscholesterol lowering eects in rats, the total serum choles-terol and triglyceride levels showed a significant reduction ascompared to the control [83]. In hypercholesterolemic malerats, fed over a four-week period with rice bran fermentedwith L. acidophilus, a significantly improved lipid profile wasobtained when compared to the control [84].

Studies with humans have shown similar results. In a10-week randomized, double-blind, placebo-controlled, andcrossover study with L. acidophilus L1 milk, there was asignificant reduction in serum cholesterol compared to theplacebo group [85]. Xiao et al. [86] evaluated the eects ofa low-fat yogurt containing B. longum BL1 in a randomized,single blind, placebo-controlled and parallel study involvingthirty-two patients. At the end of 4 weeks, the patientsshowed a significant decline in total serum cholesterol, LDL-cholesterol and triglycerides. There was also a 14.5% increasein HDL cholesterol when compared to the control.

Gastroenterology Research and Practice 7

Some studies with prebiotics have also been carried out.A randomized, double blind, and crossover study in hamstersused inulin as a prebiotic. The result was a 29% decreasein total cholesterol and a 63% decrease in triglycerides[87]. A study with 40 male Sprague-Dawley rats showeda 27% reduction in triglycerides when xylooligosaccharidewas used as a prebiotic [88]. Causey et al. [89] conducteda randomized, double-blind, and crossover study in twelvehypercholesterolemic men in order to assess the eects ofinulin in blood cholesterol. Twenty grams of inulin weregiven daily. There was a significant reduction of serumtriglycerides at the end of the 3-week study.

Synbiotics have also been evaluated for their hypocholes-terolemic eects. Twenty-four hypercholesterolemic malepigs were fed with a synbiotic formulation of L. acidophilusATCC 4962, fructooligosaccharides, mannitol, and inulin.Positive results were obtained at 8 weeks. Total plasma tri-acylglycerol, total cholesterol, and LDL levels decreased [90].Kieling et al. [91] evaluated a synbiotic yogurt containingL. acidophilus 145, B. longum 913, and oligofructose in a ran-domized, placebo-controlled, and crossover study involvingtwenty-nine women. The HDL cholesterol increased. In yetanother study, Schaafsma et al. [92] saw a significant declinein total cholesterol and LDL cholesterol in thirty volunteerswho were fed synbiotic milk containing L. acidophilus andfructooligosaccharides.

Many studies have convincingly demonstrated choles-terol-lowering eects of probiotics in both animals andhumans. However some controversial results have also beenobserved. Double blind, randomized, and crossover studiesusing L. rhamnosus LC705 [93], parallel design studies usingL. fermentum [94], and crossover studies using L. acidophilus[95] showed no change on serum lipids, triglycerides, orcholesterol. Similar controversies were also raised fromstudies evaluating the hypocholesterolemic properties ofprebiotics. When a diet with flaxseed at 1.3 g/100 g was givenin a controlled, double-blind, and crossover study, therewas no significant change in blood lipids [96]. Anotherstudy, using 20 gm/day of fructooligosaccharides for a periodof 4 weeks in type 2 diabetes patients showed no eecton glucose and lipid metabolism [57]. Similar results wereobtained on lipid modulation in a study with 18 g/day ofinulin [97]. One study using a synbiotic preparation of Lac-tobacillus acidophilus, Bifidobacterium longum, and fructo-oligosaccharides in women over a 2-month period, alsoshowed no changes in plasma concentration of total choles-terol, HDL cholesterol, LDL cholesterol, and triglyceride[98].

4.5. Cancer Prevention. As early as 1995, in a controlled,double blind study, with 138 patients a L. casei Shirotapreparation was shown to have a preventive eect on therecurrence rate of superficial bladder cancer after surgery[99]. In dierent animal models (rats and mice) fed withinulin and/or oligofructose did reduce the genotoxicity offecal water [100]. It also decreased the number of chemicallyinduced precancerous lesions [101, 102] and stimulateddefense functions. An increased level of IL-10 and of NK-cell

activity was also observed [103]. In the long term, the tumorincidence in the large intestine [104] and in other organs(breast cancer in rats and mice, metastases in the lung [105])was lowered by adding from 5 to 15% inulin or oligofructoseto the diet. This eect was even more pronounced when acombination of prebiotics and probiotics was given [106].Xylooligosaccharide was shown to reduce the number ofaberrant crypt foci in the colon of 1, 2-dimethylhydrazine-treated male Sprague-Dawley rats [88].

Some of the probiotic strains which have been/are beingused for dierent cancers, along with their references, aresummarized in Table 1.

4.6. Probiotics and Renal Health. It has been demonstratedthat gut microflora can aect the concentrations of uremictoxins in animals. Prakash and Chang were able to contin-uously reduce blood urea nitrogen in azotemic rats by oraladministration of microencapsulated genetically engineeredlive cells containing living urease-producing E. coli DH5[115]. Based on this concept, Ranganathan et al. [116]carried out rat studies using 5/6th nephrectomised animalsfed with a probiotic cocktail of Lactobacilli, Bifidobacte-ria, and S. thermophilus. Results showed a significantlyprolonged life span for the uremic rats, in addition toreduced blood urea-nitrogen (BUN) levels. Studies weresubsequently carried out in 5/6th nephrectomised Gottingenmini pigs [117]. Here also there was a reduction in BUNand creatinine levels, indicating that the probiotic supple-mentation prevented the accumulation of these toxins inthe blood. These results were further evaluated clinically byRichard Palmquist [118] in feline azotemia. Studies in 7 catsshowed statistically reduced levels in BUN and creatininelevels and demonstrated significantly improved quality oflife (QOL).The product is currently marketed for cats anddogs with moderate-to-severe kidney failure (as Azodylby Vetoquinol SA with worldwide veterinary product sales(http://www.vetoquinol.com/)).

In human studies, Simenho et al. demonstrated thathemodialysis patients whowere fed L. acidophilusNCFMhadsignificantly lower blood dimethylamine and nitrodimethy-lamine levels [119, 120]. Simenho was the first researcherto demonstrate the growth of pathogenic bacteria which isreferred to as Small Bowel Bacterial Overgrowth (SBBO).The NCFM strain is well known, and the genome hasbeen sequenced by Todd Klaenhammers group [121].Subsequent to the success of the formulation for cats anddogs described above, a similar formulation for humans wasevaluated clinically in a 6-month randomized, double-blind,placebocontrolled, and crossover trial in CKD stage 3 and4 patients in four countries [122, 123]. 46 patients werestudied in this trial. BUN levels decreased in 29 patients (P