Rapid quantification of insulin in human milk by immunoassay

Effects of Different Thawing and Warming Processes on Human Milk Composition

The composition of human milk is influenced by storage and processing practices. The effects of thawing and warming practices on human milk composition remain poorly studied despite their prevalence in home, research, and donor milk bank settings. This review comprehensively examines the impact of different thawing and warming methods on nutritional and bioactive human milk components. While some components such as carbohydrates and minerals remain stable under most typical thawing and warming conditions, others, such as fat, immune proteins, bacterial and human cells, and peptide amine hormones, are sensitive to warming. This review has identified that the data on the effects of milk thawing and warming is limited and often contradictory. Given that numerous important components of milk are diminished during cold storage, it is important that thawing and warming practices do not lead to further loss of or alterations to beneficial milk components. Further work in this field will facilitate greater standardization of thawing methods among researchers and underpin recommendations for thawing and warming of expressed milk for parents.

The impact of bed rest on human skeletal muscle metabolism

Insulin sensitivity and metabolic flexibility decrease in response to bed rest, but the temporal and causal adaptations in human skeletal muscle metabolism are not fully defined. Here, we use an integrative approach to assess human skeletal muscle metabolism during bed rest and provide a multi-system analysis of how skeletal muscle and the circulatory system adapt to short- and long-term bed rest (German Clinical Trials: DRKS00015677). We uncover that intracellular glycogen accumulation after short-term bed rest accompanies a rapid reduction in systemic insulin sensitivity and less GLUT4 localization at the muscle cell membrane, preventing further intracellular glycogen deposition after long-term bed rest. We provide evidence of a temporal link between the accumulation of intracellular triglycerides, lipotoxic ceramides, and sphingomyelins and an altered skeletal muscle mitochondrial structure and function after long-term bed rest. An intracellular nutrient overload therefore represents a crucial determinant for rapid skeletal muscle insulin insensitivity and mitochondrial alterations after prolonged bed rest.

The impact of thawing duration on leptin and adiponectin levels in frozen human milk samples

BACKGROUND

Measurements of hormone concentrations in human milk from understudied populations across the world is of growing scientific interest. Due to limited access to suitable laboratory facilities at many research sites, human milk samples are often shipped frozen to distant laboratories for analysis. Shipping and handling exposes samples to the risk of thawing and degradation as the results of delays, mishandling, or other unforeseen circumstances. Similar degradation risk factors are well known in serum samples. However, the vulnerability of hormone degradation in human milk to thawing during transportation is largely unexplored. Leptin and adiponectin are of particular importance due to their roles in feeding behavior and metabolism in infants, hence our focus on these two hormones. In addition, leptin and adiponectin have been shown to be vulnerable to pasteurization temperature degradation in human milk samples.

AIMS

We tested the degradation of human milk metabolic hormones - leptin and adiponectin - in a controlled environment in response to a variety of freeze/thaw conditions that are reflective of potential temperature fluctuations during transportation.

MATERIALS & METHODS

Human milk samples were experimentally subjected to thaw durations ranging from 4 to 16 h and assayed for hormonal levels to observe changes from baseline. Samples were also subjected to two additional experimental conditions, re-freezing after an extended period outside freezers or remaining thawed with additional ice packs, to investigate the impact of common transportation conditions.

RESULTS

We found the assayed levels of leptin were not significantly impacted by an extended thaw cycle of 16 h. However, leptin levels were impacted by the extended period of 40 h outside of the freezer. Adiponectin showed a decrease in concentration percentage after the initial 16-h thaw period, but the increased degradation between 0-16 h and 16-40 h was not as severe as that seen in the leptin samples.

DISCUSSION & CONCLUSION

The results of this experiment can be used to inform hormone measurement consistency given different thawing lengths or freezing conditions during transportation. Additionally, this research informs decisions regarding transportation, storage/handling, and data analysis in human milk research.

Nesfatin-1 in Human Milk and Its Association with Infant Anthropometry

Breastfed infants have different growth patterns to formula-fed infants and are less likely to develop obesity later in life. Nesfatin-1 is an anorexigenic adipokine that was discovered in human milk more than a decade ago, and its role in infant appetite regulation is not clear. Our aim was to describe nesfatin-1 levels in human milk collected 3-4 months postpartum, associations with infant anthropometry, and factors (maternal pre-pregnancy body mass index (mBMI), high weight gain during pregnancy, milk fat, and energy content) possibly influencing nesfatin-1 levels. We hypothesized that nesfatin-1 levels in mother's milk would differ for infants that were large (high weight-for-age Z-score (WAZ)) or small (low WAZ) at the time of milk sample collection. We used enzyme-linked immunosorbent assay to detect the nesfatin-1 concentration in milk samples from mothers to high WAZ (n = 50) and low WAZ (n = 50) infants. We investigated associations between nesfatin-1 levels and infant anthropometry at 3-4 months of age and growth since birth, using linear regression adjusted for mBMI, birth weight, infant sex, and exclusivity of breastfeeding. We found no difference in nesfatin-1 levels between the two groups and no association with infant anthropometry, even after adjusting for potential confounders. However, high nesfatin-1 levels were correlated with low mBMI. Future research should investigate serum nesfatin-1 level in both mothers, infants and associations with growth in breastfed children.

Insulin Concentration in Human Milk in the First Ten Days Postpartum: Course and Associated Factors

BACKGROUND OBJECTIVES

Human milk (HM) is better tolerated than formula in preterm infants. Insulin, which is naturally present in HM but not in formula, has been suggested as a key factor for feeding tolerance, as it appears to stimulate intestinal maturation. Its precise concentrations during the early postnatal period, however, remains unknown. The objective of this study was to assess the natural timecourse of the HM insulin concentration during the first ten days postpartum. The effect of preterm delivery, maternal obesity, and diurnal rhythm were also assessed.

METHOD

HM was collected from 31 non-diabetic mothers (21 preterm [gestational age (GA) < 37 weeks]; 10 at-term [GA ≥ 37 weeks]) on ≥ 4 time-points per day during the first five days, and once on the tenth day postpartum.

RESULTS

The HM insulin concentration declined rapidly within the first three days postpartum (day 1: 516 [312-1058] pmol/L; day 3: 157 [87-299] pmol/L), after which the concentration remained relatively stable. The insulin concentrations were higher in HM from obese mothers than from non-obese mothers (P < 0.001). Preterm delivery did not significantly affect HM insulin concentrations when adjusted for maternal pre-pregnancy body mass index category (P = 0.270). Diurnal rhythm was characterized by an insulin concentration decline throughout the night (P = 0.001), followed by an increase in the morning (P = 0.001).

CONCLUSION

The HM insulin concentration declines rapidly in the first three days postpartum, follows a diurnal rhythm, and is higher in obese mothers compared to non-obese mothers. HM insulin concentrations are not affected by preterm delivery.

Human Milk Metabolic Hormones: Analytical Methods and Current Understanding

Human milk (HM) contains a wide array of peptide hormones including leptin and adiponectin, which are involved in the regulation of infant growth and development. These essential hormones might play an important role in the regulation of metabolic reprogramming of the new-born infant. However, HM hormone studies are sparse and heterogeneous in regard to the study design, sample collection, preparation and analysis methods. This review discussed the limitations of HM hormone analysis highlighting the gaps in pre-analytical and analytical stages. The methods used to quantify HM metabolic hormones (leptin, adiponectin, ghrelin, insulin, obestatin, resistin and apelin) can be classified as immunoassay, immunosensor and chromatography. Immunoassay methods (ELISA and RIA) have been predominantly used in the measurement of these HM hormones. The relative validity parameters of HM hormones analysis are often overlooked in publications, despite the complexity and differences of HM matrix when compared to that of plasma and urine. Therefore, appropriate reports of validation parameters of methodology and instrumentation are crucial for accurate measurements and therefore better understanding of the HM metabolic hormones and their influences on infant outcomes.