Chicken Soup Inhibits Neutrophil Chemotaxis In Vitro

Barbara O. Rennard, BA; Ronald F. Ertl, BS; Gail L. Gossman, BS; Richard A. Robbins, MD, FCCP; and Stephen I. Rennard, MD, FCCP, From the Pulmonary and Critical Care Medicine Section, Nebraska Medical Center, Omaha, NE.

Disclosures

CHEST. 2000;118(4) 

In This Article

Discussion

The current study demonstrates that chicken soup inhibits neutrophil migration to standard stimuli as assessed by the modified Boyden blindwell chamber method. The effect appears to be due to an effect on the neutrophils rather than on the chemoattractant, as addition of the soup directly to the neutrophils appears to be most effective. The inhibitory effect was observed clearly at concentrations without cytotoxicity, as determined by trypan blue dye exclusion. Finally, a variety of soup preparations was evaluated and found to be variably, but generally, able to inhibit neutrophil chemotaxis. The current study, therefore, presents evidence that chicken soup might have an anti-inflammatory activity, namely, the inhibition of neutrophil migration.

The identity of the active ingredient or ingredients present in the soup remains unknown. The vegetables that are used to prepare the soup, however, are known to contain a large number of chemical species, many of which have medicinal activities. [25,26,27] A number of fats and substances with antioxidant activity are also likely to be present. Extracts of each vegetable, as well as of the chicken, all were able to inhibit neutrophil chemotaxis, suggesting that many inhibitory substances may be present. Interestingly, the vegetable extracts also demonstrated some neutrophil cytotoxicity that was not observed either in the completed soup or in the chicken extract. No attempt was made to control for concentration of various extracted components, and the toxicity could be due to a concentration-dependent effect. However, the preparation of the soup is a multistep process, and many complex chemical interactions are taking place. Determining these processes quantitatively and preparing appropriately controlled component extracts will be a challenging problem.

It is interesting, however, that neither the chicken nor the completed soup had cytotoxicity. There are several possibilities in addition to concentration effects that could explain such an effect. The chicken may contain a component that chemically neutralizes vegetable-derived toxins. Alternatively, the fat that is slowly extracted from the chicken and then skimmed from the soup surface could be extracting a lipid-soluble toxin from the preparation. That some interaction takes place during the cooking seems likely as the soup acquires maximal inhibitory activity shortly after adding the first group of vegetables. While still active, inhibitory activity does decrease slightly during the later stages of the preparation. Finally, it also is possible that the chicken could contain a component that directly activates neutrophils and has a protective effect, eg, by inducing antioxidants.

The current study assessed a single measure of the inflammatory response, migration of neutrophils by the blindwell assay method. Chicken soup inhibited chemotaxis to two different chemoattractants, ZAS, which generates the active fragment of the fifth component of complement, C5a, [24] and fMLP. [28] In vivo inflammatory responses are complex and multifaceted. Whether chicken soup has other activities remains to be determined. It was of interest, however, that while able to inhibit chemoattractant-driven migration, the soup had a slight direct chemotactic activity and may have slightly augmented nondirected migration. These effects, while statistically significant, were small and were not pursued in the current study. However, their presence suggests that chicken soup contains a multitude of moieties with diverse physiologic effects.

The chicken soup recipe used for the majority of these experiments is very highly regarded locally. [29] It does have several unusual features, however. First, it contains several vegetables, eg, sweet potato, not found in many chicken soup recipes; in addition, in many recipes, the vegetables are removed from the clear broth prior to serving. After removal, Grand-ma's soup calls for the vegetables to be pureed and added to the soup. (We understand that this was a modification introduced by Grandma during the Great Depression to ensure that everyone ate the available vegetables.) The soup, as a result, contains a thick suspension of particulates.

Particulates can interact with neutrophils and could, perhaps, interfere with chemotaxis. [30] However, for several reasons, it seems unlikely that particulates account for the majority of the activity. First, Grandma's soup, clarified by centrifugation, retained the majority of inhibitory activity. Second, Grandma's soup preparation was active prior to the addition of the pureed vegetables, the major source of particulates. Finally, inhibitory activity was observed with several other recipes that lack the vegetable particulates. Thus, while the identity of the biologically active materials is unknown, it seems likely they are water soluble or extractable.

Whether the active moieties present in chicken soup achieve sufficient concentration to be active following in vivo ingestion is not known. The identity of these moieties is not known, and bioavailability testing was beyond the scope of the current study. The activity is water extractable, however, suggesting that it may be absorbable. The inhibitory effect of chicken soup on neutrophil chemotaxis, moreover, was observed at dilutions as low as 1:200. This is comparable to the dilution of a 350-mL "average" bowl of soup eaten by a 70-kg person. The observations that activities are present in the clarified soup, are active at a dilution that was comparable to that of one bowl diluted into a body volume, and are water extractable are consistent, when taken together, with a potential in vivo effect.

Undoubtedly, the in vivo effects of chicken soup include more than the effects on neutrophils. The warm liquid, particularly when sipped, can stimulate nasal clearance and may improve upper respiratory tract symptoms. [5] The social setting in which chicken soup is often taken is likely to contribute to a strong placebo effect. Despite the observation that neutro-phil chemotactic inhibitors are present in many vegetable extracts, pureed carrots (or other vegetables) are not recommended as a remedy, while chicken soup is. This suggests that whole chicken soup may contain a mixture of active agents that synergize each other in order to achieve their beneficial effects. It is also consistent with the recommendation that the use of chickens of a certain age [1] that are, perhaps, happy [31] is more effective. Such a synergism would not be surprising, as it is certainly true for taste (this observation is from common knowledge and general experience).

Chicken soup is not without hazard. Anaphylaxis, [28] aspiration, [32,33,34] and severe electrolyte disturbances36,37 all have been described as a result of chicken soup ingestion. An anti-inflammatory effect could increase the risk for secondary infection. The benefits of chicken soup, however, are widely acclaimed and have been the subject of several reviews, [1,7] although the anecdotal nature of the clinical evidence supporting a benefit of chicken soup is well recognized.20,21 These benefits range from alleviation of symptoms of respiratory tract infection, [1,2,3,5,6,7] to possibly improving aircraft fuel usage, [37] although the data supporting some of these various claims are meager, and many of these reports lack scientific vigor. The current study was well controlled and used well-established in vitro methods to provide limited evidence that chicken soup could have an anti-inflammatory activity. Since many of the symptoms that follow upper respiratory tract viral infections may well be due to the inflammatory response, the current study may have clinical relevance.

Prolonged benefits of chicken soup also have been reported in some settings. [38] It has been suggested that even transient respiratory tract inflammation can cause prolonged worsening of asthma. [39] Should chicken soup reduce respiratory tract inflammation in vivo, there may be a prolonged benefit. It is more difficult, however, to relate the results of the present study to some of the other claims made for chicken soup, but the authors have no doubt that such speculations have been made in good taste.

The current study demonstrates a statistically significant inhibition of neutrophil chemotaxis by chicken soup in vitro. This was not an in vivo clinical trial. Whether clinical benefits would be obtained with the chicken soup used in the current study or not, therefore, remains untested. Many readers of this journal will have had personal experience with the ingestion of chicken soup in the setting of respiratory tract symptoms or other illnesses. Many clinically efficacious therapies have been discovered through careful observation. The present study provides one piece of evidence that chicken soup contains compounds of potential medical value. No doubt, many other traditional remedies do as well. The evaluation of traditional remedies by rigorous modern methods has the potential to expand our therapeutic armamentarium.

Abbreviations: fMLP = fMet-Leu-Phe; HBSS = Hank's balanced salt solution; ZAS = zymosan-activated serum

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