Opioids in milk

The protective effects of human milk-derived peptides on the pancreatic islet biology

Several epidemiological studies support the protective role of breastfeeding in reducing the risk for type 1 diabetes. Human breast milk is the perfect nutrition for infants and contains many complex proteins, lipids and carbohydrates. In this study, we examined the physiological effects of human milk-derived opioid peptides, β-casomorphins (BCM), and compared them with bovine-milk-derived opioid peptides on pancreatic hormone regulation and β-cell regeneration. Exposure of wild-type zebrafish embryos to 50 µg/ml of human BCM-5 and -7 from 3 days post fertilisation until 6 days post fertilisation resulted in an increased insulin domain of expression while exposure to bovine BCM-5 and -7 significantly reduced the insulin domain of expression as analysed by whole-mount in situ hybridisation. These changes may be accounted for by reduced insulin expression or β-cell number and were mitigated by the µ-opioid receptor antagonist, naloxone. The effect of BCM on β-cell regeneration was assessed following ablation of β-cells in Tg (ins: CFP-NTR) zebrafish from 3 days post fertilisation to 4 days post fertilisation, followed by exposure of bovine and human BCM-5 and -7 (50 µg/ml) from 4 days post fertilisation until 7 days post fertilisation. The regenerative capacity of β-cells was not impeded following exposure to human BCM-5 and -7, whereas the capacity of β-cells to regenerate following bovine BCM-5 and -7 exposure was reduced. Our data suggest that human BCM-5 and -7 may promote β-cell development and enable the regeneration of β-cells, while the bovine-milk-derived peptides, BCM-5 and -7, play an opposite role. These data may provide some biological explanation for the protective effect of breastfeeding on the development of type 1 diabetes.

An assessment of the addiction potential of the opioid associated with milk

Eighty-four male rats were tested to determine their preference for one of two distinctive places in an experimental space. After an initial determination of place preference, rats were assigned to six groups. They were then subjected to procedures to condition a place preference using doses of beta-casomorphin, a standard dose of morphine, or placebo. Subsequently, rats were tested for place preferences. No evidence emerged indicating that injections of beta-casomorphin conditioned a place preference, but evidence indicated that morphine conditioned a place preference. Consequently, systemically administered beta-casomorphin has very limited or no reinforcing properties similar to those of morphine. Ingestion of milk products containing beta-casomorphin is not likely to become the focus of an addiction.

Concomitant increase in blood plasma levels of immunoreactive hemorphin-7 and beta-endorphin following long distance running

Hemorphins are endogenous opioids derived by enzymatic degradation of hemoglobin, a protein released in blood plasma during long distance running. We examined levels of beta-endorphin and the heptapeptide hemorphin-7, in heparinized venous blood plasma from 15 sedentary controls (8 males, 7 females) and from 15 age- and sex-matched marathon runners at baseline and after running 42 km or 21 km. Baseline levels of beta-endorphin (range 0.2-4.3 fmol/ml) were neither dependent upon weight, body mass index weight/height, running status nor sex. Baseline levels of hemorphin-7 (range 0.2-6.9 pmol/ml) were lower in women (P < 0.04) and covariated positively with body weight (P = 0.06), explaining lower levels in runners by their lower body weight. Covariation with body mass index was positive, but not significant (P = 0.10), however, here the dependence upon sex appeared stronger (P = 0.014). Running induced significant and correlated increases in hemorphin-7 and beta-endorphin (r = 0.74; P < 0.002), possibly indicating a functional relationship between these two peptides.

Isolation and characterization of a hemoglobin-derived opioid peptide from the human pituitary gland

An opioid nonapeptide was isolated from fresh frozen human pituitaries. Its primary structure (Leu-Val-Tyr-Pro-Trp-Thr-Gln-Arg) was identical to fragment 32-40 of the beta-, delta-, gamma- and epsilon-chains of human hemoglobin. A larger peptide of about 4.5 kDa, which generated a fragment containing the nonapeptide on trypsin digestion, showed an amino acid composition similar to fragment 1-41 of the beta-chain of human hemoglobin. The nonapeptide interacted with mu-opioid receptors in rat brain homogenates using [3H]-(D-Ala2, MePhe3, Gly-ol5)-enkephalin and with sigma-receptors using (+)-[3H]-3-(3-hydroxyphenyl)-N-1-(propyl)piperidine, respectively. The affinities for mu-opioid receptors were in the same range as those observed for the structurally related beta-casomorphins. However, the isolated peptide showed markedly higher affinity at sigma-binding sites when compared to the beta-casomorphins or other opioid peptides. The opioid potency of this peptide as determined in the guinea-pig ileum myenteric plexus muscle preparation, was significant but less than that observed for the beta-casomorphins.

Human beta-casomorphin-8 immunoreactive material in the plasma of women during pregnancy and after delivery

A method for the extraction of human beta-casomorphin-8 immunoreactive material from human plasma and a radioimmunoassay for its determination in the plasma extracts were developed. Blood was collected from 34 men, from 35 non-pregnant women, from 35 pregnant women and from 138 women after delivery and plasma extracts were assayed for the presence of human beta-casomorphin-8 immunoreactive materials. No human beta-casomorphin-8 immunoreactive material was detected in the plasma of men or non-pregnant women, whereas such material was found in the plasma of 26 out of 35 pregnant women and in the plasma of 100 out of 138 women after parturition. Material collected from women after delivery was characterized by gel filtration and high-performance liquid chromatography (HPLC) and was found to be of different composition in various individuals; its components, one of which coeluted with human beta-casein from the HPLC column, have apparently higher molecular weights than human beta-casomorphin-8. Some of these compounds seem to be very stable against enzymatic degradation at 37 degrees C in human plasma, whereas human beta-casomorphin-8 proved to be degraded very fast under identical conditions. A physiological significance of mammary products of the beta-casomorphin type during pregnancy or after parturition is suggested.

Reduced beta-casein levels in milk samples from patients with postpartum psychosis

Defatted breast milk from women with postpartum psychosis and from healthy lactating women was analyzed by high-resolution gel permeation chromatography as well as by sodium dodecyl sulfate (SDS) and urea polyacrylamide gel electrophoresis. The gel permeation procedure allowed quantitative analysis of milk proteins (including beta-casein) with minute amounts of defatted milk (10-15 microliter). By electrophoresis, further characterization of the protein pattern, including the beta-casein fraction, was obtained. Milk samples from five control and seven psychotic subjects were analyzed. The concentration of the beta-casein-containing peak was significantly lower in milk samples from the psychotic group by both chromatography and electrophoresis. These lower levels of beta-casein may result from a higher rate of enzymatic degradation generating i.a. peptides with opioid activity, as shown earlier in plasma and CSF of women with postpartum psychosis.

beta-Casomorphin immunoreactive materials in cows' milk incubated with various bacterial species

To obtain information about the possible release of beta-casomorphins from beta-casein under in vitro conditions, cows' milk was incubated with 13 strains of Gram-negative or Gram-positive bacterial species isolated from bovine milk. After incubation periods of 1-24 d, milk samples were assayed for beta-casomorphin-4, -5, -6 or -7 immunoreactive materials. In general, no beta-casomorphin immunoreactive material was found in samples incubated with non-caseolytic strains, e.g. Pseudomonas putida or Streptococcus faecalis subsp. faecalis; however, high levels were found in several samples incubated with caseolytic strains, e.g. Ps. aeruginosa or Bacillus cereus. When such materials were present, the amounts of beta-casomorphin-4, -6 or -7 greatly exceeded beta-casomorphin-5 immunoreactivity. It was concluded that while some of these materials probably represented authentic beta-casomorphins, others were more likely to be beta-casomorphin precursors.