Uptake of Long Chain Free Fatty Acids Is Selectively Up-regulated in Adipocytes of Zucker Rats with Genetic Obesity and Non-insulin-dependent Diabetes Mellitus

Abstract

To examine whether fatty acid transport is abnormal in obesity, the kinetics of [ 3 H]oleate uptake by hepatocytes, cardiac myocytes, and adipocytes from adult male Wistar (؉/؉), Zucker lean (fa/؉) and fatty (fa/fa), and Zucker diabetic fatty (ZDF) rats were studied. A tissuespecific increase in oleate uptake was found in fa/fa and ZDF adipocytes, in which the V max was increased 9-fold (p < 0.005) and 13-fold (p < 0.001), respectively. This increase greatly exceeded the 2-fold increase in the surface area of adipocytes from obese animals, and did not result from trans-stimulation secondary to increased lipolysis. Adipocyte tumor necrosis factor-␣ mRNA levels, assayed by Northern hybridization, increased in the order ؉/؉ < fa/fa < ZDF. Oleate uptake was also studied in adipocytes from 20 -24-day-old male ؉/؉, fa/؉, and fa/fa weanlings. These animals were not obese, and had equivalent plasma fatty acid and glucose levels. Tumor necrosis factor-␣ mRNA levels in ؉/؉ and fa/fa cells also were similar. Nevertheless, V max was increased 2.9-fold (p < 0.005) in fa/fa compared ؉/؉ cells. These studies indicate 1) that regulation of fatty acid uptake is tissuespecific and 2) that up-regulation of adipocyte fatty acid uptake is an early event in Zucker fa/fa rats. These findings are independent of the role of any particular fatty acid transporter. Adipocyte mRNA levels of three putative transporters, mitochondrial aspartate aminotransferase, fatty acid translocase, and fatty acid transporting protein (FATP) were also determined; mitochondrial aspartate aminotransferase and FATP mRNAs correlated strongly with fatty acid uptake.

Differences in adipocyte long chain fatty acid uptake in Osborne–Mendel and S5B/Pl rats in response to high-fat diets

“…Adipocytes were isolated by collagenase digestion of weighed samples, 3,6 suspended in Krebs-Ringer bicarbonate/Hepes buffer containing 5% bovine albumin 21 and counted. The total number of epididymal adipocytes was calculated from the weights of the epididymal fat pads in grams and the measured cell counts per gram of tissue.…”

“…22 Fatty acid uptake studies Long chain fatty acid uptake kinetics by adipocyte suspensions were measured by rapid filtration using tracer amounts of [ 3 H]-oleic acid (OA). 3,6 As previously, 3,[6][7][8][9]23 data for OA uptake were best fitted by the sum of a saturable plus a nonsaturable function of the unbound OA concentration in the incubation medium, of the form:…”

“…Growth curve data were fitted to the model by methods of hierarchical mixed models for repeated measures, 27 assuming a first order autoregressive covariance structure (that is, the correlation between weights decreases as time between measurements increases) with SAS software (SAS Institute Inc., Cary, NC, USA), generating estimates for model parameters, designated b 0 -b 6 . The consequent interpretations are presented in Results.…”

“…Uptake occurs via two discrete processes: regulatable, protein-mediated, facilitated transport and passive flip-flop (diffusion) across the plasma membrane. [3][4][5] We have demonstrated several fold upregulation of saturable LCFA uptake in adipocytes from single-gene obesity models such as the Zucker rat, 6 ob, db, fat and tubby mouse, 7 and in dietary models of obesity in both rats and mice. 7 A similar upregulation of LCFA uptake occurs in omental adipocytes from obese patients undergoing bariatric surgery.…”

“…7 A similar upregulation of LCFA uptake occurs in omental adipocytes from obese patients undergoing bariatric surgery. 8 Upregulation of adipocyte LCFA uptake precedes onset of overt obesity in weanling Zucker rats, 6 and downregulation of adipocyte LCFA uptake precedes weight loss during leptin administration to ob mice, 9 suggesting that regulation of adipocyte LCFA uptake is a key control point for body adiposity. While these data suggest that dysregulation of adipocyte LCFA uptake might contribute to the pathogenesis of obesity, it is alternatively possible that the ability of adipocytes to upregulate LCFA uptake during caloric excess represents a buffer that protects hepatocytes, pancreatic b-cells, cardiac and skeletal muscle from LCFAmediated lipotoxicity.…”