Journal of the American College of Nutrition, Vol. 26, No. 6, 691S-694S (2007)
Published by the American College of Nutrition
Probiotics - Industry Myth or a Practical Reality?
Robert L. Clancy, MD, PhD and
Gerald Pang, PhD
Immunology, Hunter Area Pathology Service, HNEHS, John Hunter Hospital (R.L.C.)
School of Biomedical Sciences, Faculty of Health Sciences, University of Newcastle (G.P.), Newcastle, AUSTRALIA
Address reprint requests to: Prof Robert Clancy, Immunology & Microbiology, Level 4, David Maddison Clinical Sciences Building, University of Newcastle, Newcastle NSW 2308 AUSTRALIA. E-mail: Robert.clancy{at}newcastle.edu.au
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ABSTRACT
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Probiotics are "bacteria that are good for you’ evolving out of the food industry, without quality data or a framework in which to function. This review asks three questions, the answers to which dictate the level of success that probiotics have had in moving into the medical model. - How do they work? Evidence is summarised to show that (at least) certain bacteria activate Peyer's patch T cells to drive the common mucosal system via toll-like receptors on antigen presenting cells. They influence distant mucosal sites, promoting Th1 cytokine responses while downregulating Th2 responses. New data is included.
- Are all probiotics the same? They clearly are not - variation occurs between different isolates and importantly within isolates due to variable production/storage and poor quality control. These latter issues, together with poor clinical trials lacking surrogate markers of activation, have made clinical assessment very difficult.
- Do they have a role in man? Yes they do, but whether that is now or in the future largely depends on the quality of studies done. There is clear evidence in man that mucosal INF-
secretion is stimulated, indicating promotion of immune protection, downregulation of hypersensitivity disease and (yet to be demonstrated) enhanced apoptosis to reduce cancer risk. Preliminary evidence suggests that certain probiotics may regulate cytokine secretion around a mean, ensuring optimal protection without non-specific damage. Thus probiotics appear to restore defective immunity rather than stimulate, an observation relevant to restoration of Th1 immunity in infants.
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INTRODUCTION
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Probiotics have a largely deserved poor track record in health promotion, largely due to their origin as an outcome of the food industry. The marketing catchcry that probiotics are good for you lacks credibility in the era of evidenced-based medicine. Traditionally those that have studied probiotics have supported the idea that ingested probiotics have a local gut effect, through microbiological interference [1], and reviews of isolated studies on mechanism concluded that these bacterial cells stimulate immunity by increasing both secretion of INF- and the phagocytic activity of macrophages [2]. Three fundamental questions must be answered if probiotics are to contribute to health promotion in man: how do they work?; are all probiotics the same?; and do they have a role in man?
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HOW DO PROBIOTICS ACT?
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In general terms, bacterial products can stimulate both specific and non-specific immunity - indeed with most bacteria, whether taken by mouth or injected, both specific and non-specific immune outcomes can be measured. As a general rule, ingestion of non-invasive pathogens stimulates a mucosal IgA immune response in non-immune subjects, whereas in those colonised by the pathogen, IgA antibody is suppressed but there is an activation of gut-associated lymphoid tissue to selectively augment a T cell response [3]. Clinical value has been documented in both these situations - the stimulation of mucosal antibody by an oral cholera vaccine [4], and T cell-mediated protection against recurrent acute bronchitis following oral ingestion of killed non-typable Haemophilus influenzae [5]. Probiotics, however, have value through their dominant effect on the non-specific enhancement of immune function. The switch to a predominant stimulation of non-specific immunity, follows the observation that probiotic bacteria are not pathogens, but rather components of the normal gut microbes known for its contribution to host immuno-competence. The mechanism whereby probiotic bacteria promote host protection, and thus provide a framework for considering their use in promoting health, involves three levels of action. First, probiotic bacteria within the small bowel (where the number of live bacteria in effective probiotic preparations - about 1010-1011 - are of the order of the total number of bacteria within the small intestine [6]), are taken up into Peyer's patches to activate the common mucosal system. The receptor system includes toll-like receptors on antigen presenting cells (APC) [7] resulting in secretion of IL-12. Second, the pattern of cytokine secretion from T cells following APC activation and influenced by IL-12 is skewed towards a Th1 cytokine mix, characterised by INF-. This "pattern’ with high INF- secretion supports protective immunity, downregulates hypersensitivity at mucosal surfaces and enhances apoptosis retarding tumour formation. Third, T & B lymphocytes activated within the Peyer's patches enter the circulating cell pool that targets distant mucosal sites, enabling the mucosal protective effect induced by probiotic bacteria to occur at all mucosal membranes.
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DOES IT MATTER WHAT PROBIOTIC IS TAKEN?
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Yes it does. Physical characteristics such as viability, numbers, survival and colonisation in the human gut are well recognised [8]. Yet most commercial products at the time of purchase have low numbers of viable organisms with little clinical benefit. Production and quality control are outside of the "medical model’, which means that few products are likely to achieve the benefits identified in formal clinical trials. Even with better characterised isolates, trial results can vary reflecting production and stability issues. There is a major need for surrogate markers of protection to be used to monitor consistency between batches, with respect to manufacture, storage and formulation.
At the level of the individual probiotic, assumptions based on trials often suggest one or other probiotic as being optimal, without comparative studies. We have tested six commercial isolates to identify similarities and differences between different probiotic bacteria (Bifidobacterium species (2); Lactobacillus species (4)). In these studies identical numbers and conditions compare capacity to stimulate immunity both in-vitro (human monocyte - T cell blood preparations) and in-vivo (SPF eight week old female BALB/c mice). The results of these studies can be summarised:
In studies examining co-culture of different probiotic isolates with human monocyte-lymphocyte preparations (adherent monocytes and nylon wool fractionated T cells), all probiotic isolates induced high levels of IL-10. However, significantly different secretion levels of IL-12 were noted. Isolate No. 2 which stimulated the highest IL-12 level was also the most consistent stimulator of INF- (a marker of a Th1 response) [Figs. 1, 2]. When the different isolates were co-cultured with human T cells and then stimulated with the mitogen conconavalin A, there was an upregulation of INF- and a downregulation of IL-4, consistent with the mechanism described above. Again downregulation of IL-4 varied with probiotic isolate [Fig. 3]. sIgA is a classical marker of mucosal immunity. Fecal IgA measured in mice fed 1010 live bacteria daily for two weeks and tested at four weeks, showed significant variations in IgA secretion [Fig. 4]. To test variability in suppressing allergic disease, mice sensitised by an intraperitoneal injection of 2µg of ovalbumin absorbed on alum were fed 1010 live probiotic daily. The results showed total IgE was significantly depressed in mice when fed by all isolates; suppression of the OVA specific IgE antibody response, however, varied between isolates (Table 1). Airway inflammation in this mouse model following intranasal challenge with OVA (10µg per day for three days), judged as bronchial eosinophilia, again showed variation depending on which probiotic isolate was fed to the mice [Fig. 5]. There was reasonable consistency between the in-vitro and in-vivo effects with respect to the probiotic isolates. In particular, isolate No. 2 which stimulated a significantly greater amount of IL-12 (from monocytes) compared to other isolates, effectively skewed the Th1/Th2 balance with suppression of both IgE antibody and bronchial inflammation in the mouse model. It is concluded that probiotics vary with respect to their capacity to enhance and suppress hypersensitivity in-vivo, and that in-vitro models are reasonable predictors of in-vivo outcomes.
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WHAT VALUE DO PROBIOTICS HAVE IN MAN?
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In recent years clinical studies have indicated that particular probiotic preparations can protect mucosal sites against both infection [9] and damage caused by hypersensitivity to environmental allergens [10]. These studies generally lacked laboratory support and were outside of any mechanistic framework. In retrospect, however, these benefits are consistent with the immunological mechanisms discussed above. Despite the encouraging data in some studies with respect to both the prevention of mucosal infections (such as diarrhoea in Day Care Centers [9]) and the prevention and/or treatment of allergic disease [10], the literature reflects the frustrations of working with poorly standardised and non-quality controlled products, and the failure to monitor clinical outcomes with surrogate parameters of immune shift. For example a meta-analysis of protection against antibiotic associated diarrhea gave a positive result, but only 52% of the studies claimed protection [11]. Cytokine profiling should accompany all future IBS studies [12] to enable analysis of failure in terms of the particular characteristics of the isolate understudy. Yet the outcome of some clinical studies is impressive. For example, a 20 year follow-up study of non pathogenic E.coli (E.coli 083) given at birth, was associated with significant protection against both allergic disease (at 20 years) and recurrent infection (at 10 years) [13]. This study has added significance as it addresses the issue of manipulation of gut flora at that critical time of influence by enteric bacteria on the "set’ of cytokine balance, which, according to the "hygiene hypothesis’, is a determinant of subsequent allergic disease [14].
To identify cytokine surrogate markers of protection, of value in assessing probiotic clinical trials, INF- secretion and levels of this cytokine in saliva were measured in a group of athletes with impaired performance. This group was characterised by features characteristic of a reactivation of EBV infection [15]. Whole blood cultures are a simple and useful method of testing cytokine secretion potential [15]. Athletes with impaired performance had both reduced levels of INF- secretion and significantly lower values in saliva. Following daily oral therapy with a Lactobacillus acidophilus isolate there was a significant restoration to normal values, with a fourfold increase in secretion of INF- and a twofold increase in saliva levels [15]. In contrast, an interesting preliminary observation in elite athletes taking L.acidophilus, was a reduction towards the mean in INF- secretion in those with the highest INF- values [16]. Taken together, certain probiotic bacteria may have a regulatory role beyond that of simply stimulating Th1 cytokine secretion. Thus, those subjects with low secretion levels who are prone to mucosal infection respond by restoring secretion towards normal, while those with high secretion rates and an attendant risk of non-specific tissue damage due to hypersensitivity, regress downwards towards the mean. While further studies are needed to validate this homeostatic role for probiotics, the concept that gut flora can modulate immunity both upwards and down, and that defects in this function can be corrected by providing appropriate probiotic bacteria; is an intriguing clinical challenge.
It can be concluded that while a number of bacterial products available commercially as probiotics that sustain mucosal health by restoring defective immune protection (and may even act in a more extensive homeostatic function), current studies largely fall short of the standards required by a medical model. The importance of quality manufacture and formulation, and the use of surrogate laboratory markers of protection in future clinical studies, cannot be overemphasised. The use of a new term "immunobiotic’ has been suggested that best reflects a mechanistic framework describing these bacterial species [1].
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FOOTNOTES
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Disclosures: Robert Clancy and Gerald Pang have had research funds from DSM and Robert Clancy was at one time a consultant for that company.
Received August 21, 2007.
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REFERENCES
|
|---|
- Macfarlane GT, Cummings JH: Probiotics and prebiotics: can regulating the activities of intestinal bacteria benefit health? Br Med J318
:999
–1003,1999
.[Free Full Text]
- Wold AE: Immune effects of probiotics. Scand J Nutr45
:76
–85,2001
.
- Husband AJ, Dunkley ML, Cripps AW, Clancy RL: Antigen-specific response among T lymphocytes following intestinal administration of alloantigens. Aust J Exp Biol Med Sci62
:6,687
–699,1984
.
- Holmgren J, Svennerholm A: Development of oral vaccines against cholera and enterotoxigenic Escherichia coli diarrhoea. Scand J Infect Dis Suppl76
:47
–53,1990
.[Medline]
- Clancy R, Cripps A, Murree-Allen K, Yeung S, Engel M.: Oral Immunisation with killed Haemophilus influenzae for protection against acute bronchitis in chronic obstructive lung disease. Lancet Dec 21/28:1395
–1397,1985
.
- Henriksson A, Borody T, Clancy R: Probiotics under the regulatory microscope. Expert Opin Drug Saf4
:1135
–1143,2005
.[Medline]
- Christensen HR, Frokiaer H, Pestka JJ: Lactobacilli differentially modulate expression of cytokines and maturation surface markers in murine dendritic cells. J Immunol168
:171
–178,2002
.[Abstract/Free Full Text]
- Guarner F, Schaafsma GJ: Probiotics. Int J Food Microbiol39
:237
–238,1998
.[Medline]
- Isolauri E, Juntunen M, Saxilin M, Vesikari T: Lactic acid bacteria in the treatment of acute rotavirus gastroenteritis. J Pediatr Gastroenterol20
:333
–336,1995
.[Medline]
- Kalliomaki M, Salminen S, Arvilommi H, Kero P, Koskinen P, Isolauri E: Probiotics in primary prevention of atopic disease: a randomized placebo-controlled trial. Lancet357
:1976
–1079,2001
.[Medline]
- Allen S: Meta analysis in probiotic treatment of irritable bowel syndrome. Am J Gastroenterol101
:812
–817,2006
.[Medline]
- Clancy RL, Pang G, Dunkley M, Taylor D, Cripps A: Acute on chronic bronchitis: A model of mucosal immunology. Immunol Cell Biol73
:414
–417,1995
.[Medline]
- Lodinová-Zádníková R, Cukrowska B, Tlaskalova-Hogenova H: Oral administration of probiotic Escherichia coli after birth reduces frequency of allergies and repeated infections later in life (after 10 and 20 years). Int Arch All Immunol131
:209
–211,2003
.
- Sly P, Holt P: Etiological factors of atopic disease in the respiratory tract. Mucosal Immunol Update7
:13
–14,1999
.
- Clancy RL, Gleeson M, Cox A, Callister R, Dorrington M, D'Este C, Pang G, Pyne D, Fricker P, Henriksson A: Reversal in fatigued athletes of a defect in interferon- secretion after administration of Lactobacillus acidophilus. Br J Sports Med40
:351
–354,2006
.[Abstract/Free Full Text]
- Unpublished observations.
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ABSTRACT
INTRODUCTION
