**7. Probiotics and allergy: Clinical studies**

Studies have been conducted comparing the gut microbiota of infants with AD or food allergy to non-allergic infants and in these studies it was observed that allergic infants had reduced numbers of lactobacilli and bifidobacteria species in their gut (Adlerberth et al., 2007; Kirjavainen et al., 2002; Penders et al., 2007). A little more than a decade ago the first studies were published testing the hypothesis that probiotic intervention either in the pre- or post- natal period (pregnant women, offsprings or both) could influence the incidence of AD in the early years of life. Over 25 published studies have investigated similar hypotheses since then. However, these studies have largely differed in the choice of probiotic strain investigated, duration of administration of the strain, the population treated (mothers vs. newborns vs. both mothers and newborns) and in selecting the primary outcome addressing the efficacy of the trial. We have grouped the studies into 2 types- those in which the probiotic is given as a prevention strategy *i.e.* in at risk population (history of atopy in the family) and the others in which probiotics are administered as a therapeutic entity in subjects diagnosed with AD to better manage their symptoms.

#### **7.1 Prevention of AD**

Around 15 clinical trials have investigated the efficacy of probiotic in prevention of AD (summarized in Table 2). We highlight some of the more relevant well designed trials that raised key questions in the field of probiotics. Kalliomaki *et al.* conducted the first long-term preventive study on probiotics in AD and found that supplementation with the *L. rhamnosus* 


#### 334 Atopic Dermatitis – Disease Etiology and Clinical Management Probiotics and Atopic Dermatitis 335

Table 2. Prevention Studies in AD with Probiotics (R= randomized; DB= double blinded;

PC= placebo controlled)


Table 2. Prevention Studies in AD with Probiotics (R= randomized; DB= double blinded; PC= placebo controlled)

Probiotics and Atopic Dermatitis 337

GG strain both to mothers (history of atopic diseases) prenatally in the last 2-4 weeks of pregnancy and subsequently to infants from birth to 6 months significantly reduced the incidence of AD at 2 years of age, *i.e.* 15/64 subjects were confirmed AD patients in the probiotic group compared to 31/68 in the placebo control group. Interestingly enough, IgE levels and skin prick test (SPT) reactivity to common food- and aero-allergens were not different between the groups at 2 years (Kalliomaki et al., 2001). The same authors conducted a follow-up of the subjects till 4 and 7 years of age and documented the incidence of other allergic disorders (allergic rhinitis, asthma) in addition to the long term effect of probiotic treatment on AD incidence. At both the follow up time-points, *i.e.* 4 and 7 years, the incidence of AD was lower in the probiotic treated group compared to the placebo group (Kalliomaki et al., 2003; Kalliomaki et al., 2007). Yet, the incidence of respiratory allergies at the follow-up time periods seemed to be higher in the probiotic treated group. The link between probiotic administration early on in life and the development of later onset of allergies deserves to be further investigated. A subsequent study evaluating the *L. rhamnosus* GG strain in similar clinical trial settings reported no preventive effect on the development of AD at 2 years of age (Kopp et al., 2008). Possibly the beneficial effects of probiotic strains are influenced by variants such as diet and genetic heterogeneity in the target population or the strain preparation/formulation.

With the increasing interest in the field of probiotics, various strains were reported to display established or potential benefit for allergy management. In this scope, it may become important to compare the efficacy of different strains in the same clinical trial. Wickens *et al*. did exactly that and compared the efficacy of *L. rhamnosus* HN001 and *B. lactis* HN109 to a placebo; reduction in the incidence of AD at 2 years of age was observed with *L. rhamnosus* HN001 but not with *B. lactis* HN109 in comparison to the placebo, which constitutes a quite convincing result (Wickens et al., 2008). Combinations of multiple strains have also been attempted in AD clinical trials; Soh *et al.* combined two strains *B. longum* BL999 and *L. rhamnosus* GG (LPR), and found that in comparison to the placebo there was no significant effect in the reduction of AD incidence at 1 year of age (Soh et al., 2009). It should be emphasized that combination of different probiotic candidates or increasing the probiotic dose does not necessarily lead to an increased beneficial effect.

#### **7.2 Therapy: Management of AD symptoms**

Compared to prevention studies, probiotic trials in management of AD are relatively of shorter duration (typically 4-12 weeks) and aim at reducing the severity of AD. The primary outcome selected is often a change in SCORAD index which is a validated clinical scoring system that evaluates the intensity, severity of disease and quality of life parameters associated with AD symptoms. AD usually manifests at around 3-4 months of age and resolves in about 50% of the AD subjects by 2-3 years of age. As such it is often a challenge to demonstrate superiority of treatment compared to the placebo in these trials, as the baseline parameters improve spontaneously in part of the enrolled subjects since they are already on eviction diet and standardized treatments. Current data with probiotics in the management of AD is limited even though the first studies were reported almost 15 years ago (Majamaa and Isolauri, 1997).

Most studies supplement infant formulas that are extensively hydrolyzed with their choice of probiotic strains to demonstrate efficacy of probiotics over placebo (non supplemented formula). Extensively hydrolyzed formulas are a common dietary recommendation for


GG strain both to mothers (history of atopic diseases) prenatally in the last 2-4 weeks of pregnancy and subsequently to infants from birth to 6 months significantly reduced the incidence of AD at 2 years of age, *i.e.* 15/64 subjects were confirmed AD patients in the probiotic group compared to 31/68 in the placebo control group. Interestingly enough, IgE levels and skin prick test (SPT) reactivity to common food- and aero-allergens were not different between the groups at 2 years (Kalliomaki et al., 2001). The same authors conducted a follow-up of the subjects till 4 and 7 years of age and documented the incidence of other allergic disorders (allergic rhinitis, asthma) in addition to the long term effect of probiotic treatment on AD incidence. At both the follow up time-points, *i.e.* 4 and 7 years, the incidence of AD was lower in the probiotic treated group compared to the placebo group (Kalliomaki et al., 2003; Kalliomaki et al., 2007). Yet, the incidence of respiratory allergies at the follow-up time periods seemed to be higher in the probiotic treated group. The link between probiotic administration early on in life and the development of later onset of allergies deserves to be further investigated. A subsequent study evaluating the *L. rhamnosus* GG strain in similar clinical trial settings reported no preventive effect on the development of AD at 2 years of age (Kopp et al., 2008). Possibly the beneficial effects of probiotic strains are influenced by variants such as diet and genetic heterogeneity in the

With the increasing interest in the field of probiotics, various strains were reported to display established or potential benefit for allergy management. In this scope, it may become important to compare the efficacy of different strains in the same clinical trial. Wickens *et al*. did exactly that and compared the efficacy of *L. rhamnosus* HN001 and *B. lactis* HN109 to a placebo; reduction in the incidence of AD at 2 years of age was observed with *L. rhamnosus* HN001 but not with *B. lactis* HN109 in comparison to the placebo, which constitutes a quite convincing result (Wickens et al., 2008). Combinations of multiple strains have also been attempted in AD clinical trials; Soh *et al.* combined two strains *B. longum* BL999 and *L. rhamnosus* GG (LPR), and found that in comparison to the placebo there was no significant effect in the reduction of AD incidence at 1 year of age (Soh et al., 2009). It should be emphasized that combination of different probiotic candidates or increasing the

Compared to prevention studies, probiotic trials in management of AD are relatively of shorter duration (typically 4-12 weeks) and aim at reducing the severity of AD. The primary outcome selected is often a change in SCORAD index which is a validated clinical scoring system that evaluates the intensity, severity of disease and quality of life parameters associated with AD symptoms. AD usually manifests at around 3-4 months of age and resolves in about 50% of the AD subjects by 2-3 years of age. As such it is often a challenge to demonstrate superiority of treatment compared to the placebo in these trials, as the baseline parameters improve spontaneously in part of the enrolled subjects since they are already on eviction diet and standardized treatments. Current data with probiotics in the management of AD is limited even though the first studies were reported almost 15 years

Most studies supplement infant formulas that are extensively hydrolyzed with their choice of probiotic strains to demonstrate efficacy of probiotics over placebo (non supplemented formula). Extensively hydrolyzed formulas are a common dietary recommendation for

target population or the strain preparation/formulation.

**7.2 Therapy: Management of AD symptoms** 

ago (Majamaa and Isolauri, 1997).

probiotic dose does not necessarily lead to an increased beneficial effect.


Table 3. Management studies in AD with probiotics (R= randomized; DB= double blinded;

PC= placebo controlled)


Table 3. Management studies in AD with probiotics (R= randomized; DB= double blinded; PC= placebo controlled)

Probiotics and Atopic Dermatitis 341

allergic diseases and the conclusions of this work have been published (The journal of Nutrition, 140, Number 3S-I, supplement). Potential avenues for optimizing clinical trials in the field of probiotics and allergy, and caveats that may lead to misinterpretation of

A few studies point to the fact that probiotics may work only on IgE-mediated AD. These results although are based on (often retrospective) sub-grouping of the target population into IgE vs. non-IgE groups. Clinical trials are needed in the future specifically in large

Even though several probiotic candidate strains have been tested *in vitro* and in preclinical models of AD, it remains difficult to discuss the predictive value of these preclinical studies. Indeed there has not been sufficient alignment between the strains used for clinical trials and the ones used for preclinical studies. However, the preclinical models can certainly serve the purpose of (i) further understanding the mechanisms of action of specific strains that have been found to be beneficial in AD clinical trials, (ii) evaluating the best intervention window(s) (prenatal, perinatal, weaning, later in life), (iii) performing doseresponse curves and (iv) analyzing the impact of probiotic preparation/formulation or inclusion in a final product, to assess combinations of anti-allergy ingredients, and (v) supporting the dossier to submit for approval by ethical committees for human trials. In conclusion, when analyzing the results of past and ongoing clinical trials performed with probiotics and allergy, it should be kept in mind that AD is a complex multifactorial disease whose onset or outcome may strongly depend on the complex interplay between the host, in particular its genetic background, the status of the immune system and intestinal microbiota, and environmental factors. Nevertheless, additional efforts in the area deserve to be pursued as nutritional interventions remain by themselves an interesting approach to

We warmly thank Dr Carine Blanchard for critical review of the chapter and her

Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of

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overall results were outlined (Kalliomaki et al., 2010).

manage allergic manifestations.

**9. Acknowledgements** 

suggestions.

**10. References** 

enough cohorts of IgE-mediated AD to substantiate this hypothesis.

infants with AD manifestations linked to cow's milk allergy and are largely effective in reducing the severity of AD. To demonstrate an improvement with probiotic supplementation is by itself a challenging primary outcome. Different strains have been evaluated in pilot clinical trials (Table 3) with mixed results. Isolauri *et al.* showed that both *L. rhamnosus* LGG and *B. lactis* Bb12 were effective in reducing the severity of AD (Isolauri et al., 2000). Interestingly, in a recent publication LGG was however shown to have no effect on AD severity (Nermes et al., 2011).

The selection of the target population also plays a major role in the success of these trials. Weston *et al.* demonstrated the efficacy of *L. fermentum* PCC in a cohort of subjects with moderate to severe AD while other studies have typically selected mild to moderate AD subjects and have not succeeded in showing the efficacy of the probiotic strains (Weston et al., 2005). Combinations, with other strains or with prebiotics have been attempted with a variable success. For example, van der Aa *et al.* evaluated a combination of *B. breve* M-16V with a prebiotic mixture. After 12 weeks, the severity of atopic dermatitis (AD) did not differ between the two groups, indicating no superiority of the synbiotic combination of (pro- and pre-biotic) over placebo (van der Aa et al., 2010).
