Pancreatic steatosis and its relationship to β-cell dysfunction in humans: racial and ethnic variations

Ectopic fat deposition in prediabetic overweight and obese minority adolescents

CONTEXT

Optimizing effective prevention and treatment of type 2 diabetes in youth is limited by incomplete understanding of its pathophysiology and how this varies across ethnicities with high risk.

OBJECTIVE

The aim of this study was to examine the contribution of visceral adipose tissue (VAT), hepatic fat fraction (HFF), and pancreatic fat fraction (PFF) to prediabetes in overweight/obese African American (AA) and Latino youth.

DESIGN AND SETTING

We conducted a cross-sectional study in an academic pediatric care facility.

SUBJECTS

A total of 148 healthy, overweight/obese adolescents (56 AA, 92 Latino; 72 males, 76 females; age, 15.5 ± 1.2 y; BMI z-score, 2.1 ± 0.5) participated in the study. They were normal glucose tolerant (n = 106) and prediabetic (n = 42), based on fasting glucose of 100-125 mg/dL and/or 2-hour glucose of 140-199 mg/dL, and/or hemoglobin A1C 6.0-6.4%.

MAIN OUTCOME MEASURES

We measured sc abdominal adipose tissue, VAT, HFF, and PFF by 3-Tesla magnetic resonance imaging and measured total body fat by dual-energy x-ray absorptiometry.

RESULTS

Adolescents with prediabetes had 30% higher HFF (P = .001) and 31% higher PFF (P = .042), compared to those with normal glucose tolerance after controlling for age, sex, pubertal stage, ethnicity, total percentage body fat, and VAT. Logistic regression showed that PFF predicted prediabetes in AAs and HFF predicted prediabetes in Latinos, with the odds of having prediabetes increased by 66% for every 1% increase in PFF in African Americans, and increased by 22% for every 1% increase in HFF in Latinos.

CONCLUSION

These data demonstrate that ectopic fat phenotypes associated with prediabetes are established by adolescence. Ethnic differences in the deposition of ectopic fat in adolescents with prediabetes may differ, with pancreatic fat in AAs, vs hepatic fat in Latino adolescents, being associated with diabetes risk.

Measurement of pancreatic volume by abdominal MRI: a validation study

Objective

To develop abdominal magnetic resonance imaging (MRI) protocol to measure pancreatic volume in humans and to validate it in large animals.

Materials and Methods

We performed abdominal MRI in eight mini-pigs using a clinical 3T MRI system. We used consecutive parallel abdominal slices, covering the entire pancreas to calculate pancreatic volume. Following MRI, animals were sacrificed, the pancreas was removed, and the volume of the pancreas was measured by water displacement. We used the same MRI protocol to measure pancreatic volume in 21 humans. To assess reproducibility of in vivo measurement we repeated MRI pancreas volume evaluation within 24 hours in additional five humans.

Results

In mini-pigs the measurements of pancreatic volume by MRI and by water displacement were almost identical (R² = 0.9867; p<0.0001). In humans the average pancreas volume was 72.7+/−4.5 ml, range from 35.0 to 105.5 ml. This result is in strong agreement with results of previous large postmortem and computed tomography (CT) studies. Repeated measurements of pancreatic volume in humans were highly reproducible. Pancreatic volume measured in vivo was negatively correlated with age, body fat mass, pancreatic TG levels, and visceral fat mass.

Conclusions

These initial results are highly encouraging and our protocol for pancreatic volume estimation in vivo may prove useful in obesity research to follow in vivo changes of pancreatic volume and structure during time course of obesity and type 2 diabetes development.