The exogenous opioid peptides and DPPIV serum activity in infants with apnoea expressed as apparent life threatening events (ALTE)
Introduction
Sudden infant death syndrome (SIDS) is an important cause of deaths in infants (Carpenter et al., 2004). SIDS is recognized when an infant dies suddenly, in a way that cannot be expected by his or her history, and without a cause found during a forensic autopsy or thorough a death-scene investigation (Beckwith, 2003). In the multi-factorial pathogenesis of SIDS, participation of the following factors is stressed the most: neurological prematurity, respiratory infection, genetic factors and anaemia-related apnoea (Mage and Donner, 2009). Most susceptible to SIDS are infants exposed to several postnatal factors: prone sleep position, passive smoking and high sleep-room temperature (Blair et al., 2009, Jorch et al., 2007).
It is supposed that in some cases of SIDS, it is cows’ milk that may play a certain role. It is also suspected that β-casomorphins hold a direct responsibility for that situation (Storm et al., 1990). β-Casomorphins (BCMs) are opioid-like peptides (the chain length of 4–11 amino acids) released from β-casein of bovine or human milk during technological processes and/or enzymatic digestion in the intestine (Jarmolowska et al., 2007c, Kostyra et al., 2004, Sienkiewicz-Szlapka et al., 2009a). BCMs are biologically active towards μ-opioid (MOP) receptor agonist with effects similar to that of morphine. MOP receptors are found primarily in the central nervous system and the gastrointestinal tract and play an important role in responding to stress and pain, as well as in controlling food intakes (Teschemacher, 2003). Penetration of β-casomorphins into the infant’s immature central nervous system may inhibit the respiratory centre in the brainstem leading to abnormal ventilatory responses, hypercapnia, hypoxia, apnoea and death (Sun et al., 2003). Detection of casomorphin-immunoreactive material in the brainstem of infants who died of SIDS points at BCMs as one of potential causes of SIDS (Pasi et al., 1993).
A high-proline structure of bovine β-casomorphins makes them resistant to proteolytic enzymes (Kreil et al., 1983). However, their inactivation may be rapidly accomplished by the use of dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) (Tiruppathi et al., 1990). DPPIV is a highly specialized membranous aminopeptidase that releases dipeptides from N-terminus of peptides with proline or alanine (rarely) in the penultimate position. It also performs functions of a receptor and a co-stimulatory protein, as well as is involved in the processing of adhesion and apoptosis (Boonacker and Van Noorden, 2003, Durinx et al., 2000). Its activity can be detected in epithelium/endothelium cells of all tissues (mainly in the liver, intestine, and kidneys), in the immune cells, in the meconium. A soluble form of this enzyme appears in the serum, urine, seminal plasma and amniotic fluid (Boonacker and Van Noorden, 2003, Caporale et al., 1985, Jarmolowska et al., 2007a, Jinsmaa and Yoshikawa, 1999). Due to its multifunctional character and its widespread expression, the exact functions of DPPIV in vivo have not yet been fully elucidated. One of the known things is that DPPIV plays a key role in modification, processing and/or inactivation of peptides, e.g. peptide hormones, various cytokines, chemokines, neuropeptides, growth factors and some biologically active peptides derived from food like β-casomorphins (Cohen et al., 2004, Mentlein, 1999, Tiruppathi et al., 1990).
Due to the fact that results obtained by some of researchers indicate a relationship between consumption of milk and apnoea in infants who died of SIDS, there is a probability that a similar connection may occur in children with a high risk of SIDS (‘near miss SIDS’) (Dunne and Matthews, 1987). Those are infants with ALTE – apparent life threatening events – that required a vigorous stimulation or a mouth-to-mouth resuscitation. ALTE is not a definitive diagnosis: it involves symptoms such as episodes of apnoea, a change of the skin and lips colour (pallor or cyanotic), muscle weakness and limpness, choking and gagging that may occur suddenly. Approximately 10% of ALTE infants die of SIDS and approximately 50% of hospitalized ALTE infants have various gastrointestinal disorders recognized (Kahn, 2004). Those disorders may predispose the infants to adverse reactions to foreign proteins. There is no published data on β-casomorphin contents in sera of infants with apnoea. Therefore, the aim of this study was to determine the contents of bovine β-casomorphin-7 and activity of the enzyme that hydrolyses this peptide, dipeptidyl peptidase-IV (DPPIV) in sera of ALTE infants.
Section snippets
Chemicals
Acetonitrile (HPLC grade) and trifluoroacetic acid (TFA) were purchased from J.T. Baker (Witko, Poland). The remaining chemicals, at least those of an analytical grade, were purchased from Sigma–Aldrich Poland (Poznań, Poland). Bovine β-casomorphin-7 (Tyr-Pro-Phe-Pro-Gly-Pro-Ile) was custom-synthesized at the University of Gdańsk (Gdańsk, Poland).
Characteristics of ALTE patients
The study included 17 infants, aged 2–7 months, hospitalised due to occurrences of life-threatening events at the 3rd Clinic of Children’s Diseases of
β-Casomorphin-7 content in the infants’ sera
The qualitative and quantitative determination of the content of bovine BCM-7 has been conducted with a competitive ELISA. To perform it, obtaining specific antibodies was necessary. The rabbit immunization yielded polyclonal antisera with titters about 1:5000, from which IgG preparations were obtained. The specificity test showed a high selectivity for the antibodies. There were no cases of cross-reactivity between the specific antibodies and the other opioid peptides (bBCM-5, bBCM-6, hBCM-5
Discussion
Ingredients that are contained in food are responsible for children’s development both in their foetal and postnatal life. The role of food ingredients is of particular importance during the first months of their adaptation to new life conditions. It is the time when milk makes the only food and oligopeptides released from the milk proteins may manifest systemic activities. β-Casomorphins, which exhibit an opioid activity, are ones of such proteins. Species-specific β-casomorphins (hBCMs) have
Conclusions
We have observed in our research that permeating of the biologically active peptide, bBCM-7 may be of general character but its highest concentrations are present in infants of the ALTE group fed with formulas containing casein. In all the infants with the diagnosed ALTE syndrome, we have observed a definitely lower activity of serum dipeptidyl peptidase IV, which may be their specific feature. The presence of bBCM-7 in the infants’ blood sera combined with the low DPPIV activity may favour
Ethics
The study has been approved by the Human Research Ethics Committee at the Medical University at Bialystok. Informed consents have been obtained from the all children’s parents.
Conflict of Interest
None of the authors have reported any biomedical financial interests or potential conflicts of interest.
Acknowledgments
The authors would like to thank sincerely all the children and parents who participated in this study.
The research was conducted under projects financed by the Ministry of Science and Higher Education number N 407 058 32/2527.
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