Blood leptin homeostasis: sex-associated differences in circulating leptin levels in rats are independent of tissue leptin expression

Circulating leptin levels are higher in women than in men. The aim of the study has been to determine in rats the putative existence of sex-associated differences in leptin expression in different adipose tissue depots (gonadal, retroperitoneal, mesenteric and inguinal white adipose tissue and interscapular brown adipose tissue) and the relationship with circulating leptin levels. Adult male and female Wistar rats acclimated to 22 degrees C or to 28 degrees C were used. Leptin mRNA expression was assessed by northern blot and serum leptin levels by enzyme-linked immunosorbent assay (ELISA). Contrary to what happens in humans, we report here that male rats acclimated to standard animal house conditions (22 degrees C) have a higher leptin concentration in blood than female rats. This situation cannot be explained by a greater size of the fat depots in males, because the adiposity index is similar in both genders, but are rather associated to higher leptin specific mRNA expression by the white adipose tissue. Around thermoneutral conditions (28 degrees C), sex related differences in leptin mRNA expression disappear, but the gender difference in circulating leptin levels remains. In addition, leptin mRNA expression is higher in both genders in thermoneutral conditions but this is not reflected in changes in the circulating leptin levels. In conclusion, this study shows that rat circulating leptin levels are finely regulated, and not exclusively dependent on leptin mRNA expression, but other mechanisms are also involved, possibly regarding leptin rate of degradation.     

Resistin expression in different adipose tissue depots during rat development

Resistin is a hormonal factor synthesised by adipocytes that was first thought to be related with the resistance to insulin in obesity, but whose function is not yet completely established. Here we have studied the ontogenic pattern of resistin mRNA expression in different white adipose tissue depots (WAT) – epididymal, inguinal, mesenteric and retroperitoneal – and in brown adipose tissue (BAT), as well as the circulating resistin levels, in rats of different ages (from the suckling period to one year of age). Resistin mRNA was determined by Northern blotting, and serum levels by enzyme immunoassay. In WAT, resistin expression remains almost constant with age, except in early development, where there is a peak of expression in the epididymal and retroperitoneal depots, and a decrease in the inguinal one, while the expression remains constant for the mesenteric depot. Moreover, there is a site-specific difference regarding resistin expression: all the depots express characteristic levels of mRNA, especially at the age of 2 months, the moment when resistin mRNA levels are significantly higher in the epididymal and the retroperitoneal than in the inguinal and mesenteric WAT and than in the BAT. The transient increased resistin expression in the epididymal and the retroperitoneal WAT at a period of time in which there is a change in diet (from milk to chow) suggests a common nutritional regulation of the resistin gene. Circulating resistin levels increase with age probably reflecting the increase in the body fat content.     

Effect of oscillatory high hydrostatic pressure treatments on Byssochlamys nivea ascospores suspended in fruit juice concentrates

The effect of continuous (689 MPa with holding times of 5, 15 or 25 min) and oscillatory (one, three or five cycles at 689 MPa with holding times of 1 s) high hydrostatic pressure treatments on the viability of Byssochlamys nivea ascospores suspended in apple and cranberry juice concentrates adjusted by dilution to water activities (a_w) of 0·98 and 0·94 was evaluated at 21 and 60 °C. Inactivation of the initial spore inocula was achieved after three or five cycles of oscillatory pressurization at 60 °C when the a_w was 0·98 in both fruit juices. With a_w 0·94, the initial inocula were reduced by less than 1 log-cycle after five pressure cycles. Inactivation was not observed within 25 min with continuous pressurization at 60 °C. In treatments at 21 °C, no effect on spore viability was observed with continuous or oscillatory treatments.     

Milk Leptin Surge and Biological Rhythms of Leptin and Other Regulatory Proteins in Breastmilk

A significant number of chronic diseases are linked to perinatal nutrition, and prevention may be associated to naturally occurring components of breast milk. One key hormone in breast milk is leptin, related with the protection from obesity in the adulthood, thus knowing its changes through the day or lactation is crucial. We aimed to investigate the daily rhythms in the milk levels of leptin, together with other two related hormones, ghrelin and adiponectin, during lactation (days 5, 10 and 15) in rat dams, and the relation with morphometric parameters (dams and pups). Summarizing the main results, the existence of biological rhythms, but not daily and maybe circasemidian, was confirmed for the three hormones at the earliest period of lactation. The correlations performed generally showed a possible dependence of milk hormone levels on plasma levels at the early phase of lactation, while with the progression of lactation this dependence may fade and the hormone levels are suggested to be more dependent on mammary gland production/maturation. There was also a correlation between milk leptin and adiponectin levels, especially in the first half of lactation, suggesting a possible parallel regulation. Interestingly, we describe a milk leptin surge around the mid of lactation (at day 10) which may be related with pup´s growth (males and females) and with the well-known (in the literature) plasma leptin surge in pups. All this knowledge may be crucial for future applications in the development of formula milk and in relation with the role of leptin surge during lactation.     

Conjugated Linoleic Acid Supplementation under a High-Fat Diet Modulates Stomach Protein Expression and Intestinal Microbiota in Adult Mice

The gastrointestinal tract constitutes a physiological interface integrating nutrient and microbiota-host metabolism. Conjugated linoleic acids (CLA) have been reported to contribute to decreased body weight and fat accretion. The modulation by dietary CLA of stomach proteins related to energy homeostasis or microbiota may be involved, although this has not been previously analysed. This is examined in the present study, which aims to underline the potential mechanisms of CLA which contribute to body weight regulation. Adult mice were fed either a normal fat (NF, 12% kJ content as fat) or a high-fat (HF, 43% kJ content as fat) diet. In the latter case, half of the animals received daily oral supplementation of CLA. Expression and content of stomach proteins and specific bacterial populations from caecum were analysed. CLA supplementation was associated with an increase in stomach protein expression, and exerted a prebiotic action on both Bacteroidetes/Prevotella and Akkermansia muciniphila. However, CLA supplementation was not able to override the negative effects of HF diet on Bifidobacterium spp., which was decreased in both HF and HF+CLA groups. Our data show that CLA are able to modulate stomach protein expression and exert a prebiotic effect on specific gut bacterial species.     

Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected a(w) and pH

AIM: To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound. METHODS AND RESULTS: Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (a(w); 0.99 or 0.97) and pH (5.5 or 4.5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at a(w) 0.99, and pH 5.5 to 100-ppm thymol or carvacrol for the four studied bacteria at a(w) 0.97 and pH 4.5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the a(w) and the pH tested. CONCLUSIONS: Synergistic binary mixtures with fractional inhibitory concentration index <0.6 include 100- or 200-ppm potassium sorbate with 50- or 100-ppm thymol, carvacrol or eugenol. SIGNIFICANCE AND IMPACT OF THE STUDY: The synergistic combinations could be useful in reducing the amounts of antimicrobials needed to inhibit growth, thus diminishing consumer concerns regarding chemical preservatives.