Ammonium uptake and urea production in hepatocytes from lean and obese Zucker rats

Plasma metabolomic profiling suggests early indications for predisposition to latent insulin resistance in children conceived by ICSI

BACKGROUND

There have been increasing indications about an epigenetically-based elevated predisposition of assisted reproductive technology (ART) offspring to insulin resistance, which can lead to an unfavorable cardio-metabolic profile in adult life. However, the relevant long-term systematic molecular studies are limited, especially for the IntraCytoplasmic Sperm Injection (ICSI) method, introduced in 1992. In this study, we carefully defined a group of 42 prepubertal ICSI and 42 naturally conceived (NC) children. We assessed differences in their metabolic profile based on biochemical measurements, while, for a subgroup, plasma metabolomic analysis was also performed, investigating any relevant insulin resistance indices.

METHODS & RESULTS

Auxological and biochemical parameters of 42 6.8±2.1 yrs old ICSI-conceived and 42 age-matched controls were measured. Significant differences between the groups were determined using univariate and multivariate statistics, indicating low urea and low-grade inflammation markers (YKL-40, hsCRP) and high triiodothyronine (T3) in ICSI-children compared to controls. Moreover, plasma metabolomic analysis carried out for a subgroup of 10 ICSI- and 10 NC girls using Gas Chromatography-Mass Spectrometry (GC-MS) indicated clear differences between the two groups, characterized by 36 metabolites linked to obesity, insulin resistance and metabolic syndrome. Notably, the distinction between the two girl subgroups was accentuated when both their biochemical and metabolomic measurements were employed.

CONCLUSIONS

The present study contributes a large auxological and biochemical dataset of a well-defined group of pre-pubertal ICSI-conceived subjects to the research of the ART effect to the offspring's health. Moreover, it is the first time that the relevant usefulness of metabolomics was investigated. The acquired results are consistent with early insulin resistance in ICSI-offspring, paving the way for further systematic investigations. These data support that metabolomics may unravel metabolic differences before they become clinically or biochemically evident, underlining its utility in the ART research.

Catabolism of amino acids in livers from cafeteria-fed rats

Most studies using a hypercaloric diet to induce obesity have focused on the metabolism of fat and carbohydrates. Less concern has been given to the metabolism of amino acids, despite evidence of modifications in nitrogen metabolism during obesity. The aim of this study was to evaluate amino acid metabolism in livers from cafeteria diet-induced obese rats. Blood parameters were analysed, and histological sections of livers were stained with Sudan III. The enzymatic activities of some enzymes were determined in liver homogenates. Gluconeogenesis, ureagenesis, and oxygen consumption were evaluated in rat livers perfused with glutamine, alanine, or ammonium chloride. Compared to control rats, cafeteria-fed rats demonstrated higher levels of triacylglycerol and glucose in the blood and greater accumulation of fat in livers. Gluconeogenesis and urea production in livers perfused with glutamine and alanine at higher concentrations showed a substantial reduction in cafeteria-fed rats. However, no significant difference was observed among groups perfused with ammonium chloride. The activities of the enzymes alanine aminotransferase, glutaminase, and aspartate aminotransferase in the livers were reduced in cafeteria-fed rats. Taken together, these data are consistent with the hypothesis that livers from cafeteria diet-induced obese rats exhibit a limitation in their maximal capacity to metabolise glutamine and alanine to glucose, ammonia, and urea, not because of an impairment in gluconeogenesis and/or ureagenesis, but rather due to a depression in the activities of enzymes that catalyse the initial steps of amino acid metabolism.

Hepatocyte transplantation from steatotic liver in a rat model

BACKGROUND

Hepatocyte transplantation (HTx) has progressed significantly, but widespread application remains slow because of the shortage of donor hepatocytes. Many sources of hepatic cells have been proposed as alternatives to isolated hepatocytes, but primary isolated hepatocytes continue to be the best source for liver cell-based therapy. To expand the donor pool, we focused on steatotic liver as a new cell source for HTx because numerous steatotic livers are discarded as unsuitable for orthotopic liver transplantation. This study investigated the efficacy of steatotic hepatocyte transplantation (SHTx) using steatotic liver in a rat model.

MATERIALS AND METHODS

Hepatocytes were isolated from obese and lean Zucker rats. Hepatocytes from each group were cultured to analyze the function of steatotic hepatocytes. Hepatocytes from each group were also transplanted into the spleens of Nagase analbuminemic rats (NARs) to investigate the efficacy of SHTx.

RESULTS

In the in vitro experiment, a real-time reverse-transcription polymerase chain reaction assay showed that albumin and several hepatocyte nuclear factors were highly expressed in both groups. Morphologically, the steatotic hepatocytes were positive for albumin, and an enzyme-linked immunosorbent assay showed no significant differences between the two groups except for albumin production after 5 d of culture. In the in vivo experiment, the transplanted steatotic hepatocytes in the spleens of Nagase analbuminemic rats were positive for albumin and periodic acid-Schiff staining. Surprisingly, an enzyme-linked immunosorbent assay showed no significant differences in the serum albumin levels between the two groups throughout the study period.

CONCLUSIONS

We have demonstrated that steatotic hepatocytes are a potential new cell source for HTx therapy.