Fatty liver disease, glucose tolerance and insulin resistance in obese adolescents

BACKGROUND/OBJECTIVES

Adult studies suggest that intra-hepatic fat predicts 2-h blood glucose levels and type 2 diabetes, and may have a role in the development of insulin resistance. Our study objective was to explore relationships between intra-hepatic fat and (i) blood glucose levels and (ii) insulin resistance determined by homeostasis model assessment (HOMA) in a group of obese adolescents.

METHODS

Subjects were 61 obese non-diabetic male and female volunteers aged 12-18 years inclusive with a body mass index >95th percentile for age and 2-h blood glucose <200 mg dL(-1) . Each subject underwent 2-h glucose tolerance testing and measurement of haemoglobin A1c, ultrasensitive C-reactive protein and fasting insulin. Visceral, subcutaneous abdominal and intra-hepatic fat were determined by magnetic resonance imaging. Intra-hepatic fat was measured by gradient echo chemical shift imaging.

RESULTS

Alanine aminotransferase levels and hepatic phase difference were not significant correlates of fasting or 2-h glucose. In a multiple regression model including hepatic phase difference and visceral fat volume, visceral fat volume was the sole predictor of HOMA.

CONCLUSIONS

This study provides no support to the notion that intra-hepatic fat has a role in the regulation of fasting blood glucose, 2-h postprandial blood glucose or systemic insulin resistance.

Hereditary elliptocytosis due to both qualitative and quantitative defects in membrane skeletal protein 4.1

Protein 4.1 is an important structural component of the membrane skeleton that helps determine erythrocyte morphology and membrane mechanical properties. In a previous study we identified a case of human hereditary elliptocytosis (HE) in which decreased membrane mechanical stability was due to deletion of 80 amino acids encompassing the entire 10-Kd spectrin-actin binding domain. A portion of this domain (21 amino acids) is encoded by an alternatively spliced exon that is expressed in late but not early erythroid cells. We now report a case of canine HE in which the abnormal phenotype is caused by failure to express this alternative peptide in the mature red blood cell (RBC) membrane skeleton, in conjunction with quantitative deficiency of protein 4.1. Western blotting of RBC membranes from a dog with HE showed a truncated protein 4.1 that did not react with antibodies directed against the alternative peptide. In addition, sequencing of cloned reticulocyte protein 4.1 cDNA showed a precise deletion of 63 nucleotides comprising this exon. Normal dog reticulocytes did express this exon. Expression of this 21 amino acid peptide during erythroid maturation is therefore essential for proper assembly of a mechanically competent membrane skeleton, because RBCs lacking this peptide have unstable membranes.