Search PubMed⌕ Search

Biomedical subjects

R H Eckel

Publications and source records attributed to R H Eckel.

At least 37 records · Page 2Linked to original sources
PubMed2000

Increased intracellular triglyceride in C(2)C(12) muscle cells transfected with human lipoprotein lipase.

Much of the knowledge about the cell biology of lipoprotein lipase (LPL) in vitro has been gained from adipose tissue model systems. However, the importance of skeletal muscle lipoprotein lipase (SMLPL) to both lipoprotein and muscle metabolism remains unclear. Although the production of LPL in cultured myocytes has been documented, the amount of enzyme activity produced is small. To develop a more suitable tissue culture model for SMLPL, mouse C(2)C(12) myoblasts were stably transduced with a retroviral vector encoding the full-length human LPL (hLPL) cDNA. Control cells were transduced with a vector encoding beta-galactosidase. LPL expression was assayed as a function of cell growth by measuring LPL activity on days 3, 7, 9, 11, and 14 after subculture. The hLPL-transduced myoblasts increasingly overexpressed both heparin-releasable (HR) and intracellular (IN) LPL activity compared to nontransduced myoblasts (P < 0.001 at Day 11) and myoblasts transduced with the control vector (P < 0.001 at Day 11). This increase occurred while LPL mRNA levels remained stable between days 3 and 14. As expected, IN LPL activity was also increased in the transduced cells. High levels of LPL activity were also obtained after differentiating the C(2)C(12) cells into myotubes by serum deprivation. Additionally, throughout the time course, C(2)/LPL cells had greater amounts of intracellular triglyceride than both the C(2)C(12) and the C(2)/beta-GEO cells (P = 0.005 and P < 0.001, respectively) with the largest differences seen on day 14 of the time course (P = 0.001, C(2)/LPL vs C(2)C(12) (r) or C(2)/beta-GEO cells). Thus, C(2)C(12) myoblasts stably transduced with hLPL markedly overexpressed both HR and IN LPL activity compared to control cells which, in turn, was associated with increases in intracellular triglyceride content. Because LPL regulation in tissues is mostly posttranslational, this new in vitro model will permit the in-depth study of the posttranslational regulation of SMLPL and provide new insights into the fate of lipoprotein-derived fatty acids in muscle.

Animals↗
PubMed2000

Obesity resistance and multiple mechanisms of triglyceride synthesis in mice lacking Dgat.

Triglycerides (or triacylglycerols) represent the major form of stored energy in eukaryotes. Triglyceride synthesis has been assumed to occur primarily through acyl CoA:diacylglycerol transferase (Dgat), a microsomal enzyme that catalyses the final and only committed step in the glycerol phosphate pathway. Therefore, Dgat has been considered necessary for adipose tissue formation and essential for survival. Here we show that Dgat-deficient (Dgat-/-) mice are viable and can still synthesize triglycerides. Moreover, these mice are lean and resistant to diet-induced obesity. The obesity resistance involves increased energy expenditure and increased activity. Dgat deficiency also alters triglyceride metabolism in other tissues, including the mammary gland, where lactation is defective in Dgat-/- females. Our findings indicate that multiple mechanisms exist for triglyceride synthesis and suggest that the selective inhibition of Dgat-mediated triglyceride synthesis may be useful for treating obesity.

Absorption↗
PubMed2000

Orlistat fails to alter postprandial plasma lipid excursions or plasma lipases in normal-weight male volunteers.

OBJECTIVES: After 10 d of orlistat administration (120 mg three times/day), the primary objective was to determine the drug's effect on postprandial plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activities on day 10 after an oral fat-load. The secondary objectives were to determine the effects of orlistat on 12 h postprandial measures of: (1) preheparin HTGL and LPL; and (2) serum triglycerides, very-low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and free fatty acids. METHODS: Twenty-four normal-weight, healthy male volunteers were randomized to either 120 mg orlistat (n=12) or placebo (n=12) three times a day with meals for 10 d. Preheparin LPL and HTGL activities and LPL specific activity were measured in the fasted state on days 1, 5, and 10. On days 5 and 10 the study medication (orlistat or placebo) was taken at the beginning of a fat-rich breakfast and serum lipid and lipoprotein levels monitored for 12 h postprandially. On day 10, 15 min postheparin HTGL activity was measured 8 h after the fat-rich breakfast. RESULTS: No differences were found between groups in fasting levels of preheparin LPL or HTGL activity or in LPL-specific activity on days 1, 5 and 10. No difference was found between the two treatment groups in postheparin HTGL activity 8 h after the fat-rich breakfast. Also, no differences were found between the two groups in plasma triglycerides or lipoproteins. CONCLUSION: The results indicate that the oral administration of orlistat (120 mg t. i.d.) does not significantly alter plasma triglycerides or lipoproteins, and that the inhibitory effect of orlistat on lipases is limited to the gastrointestinal tract and is not manifested systemically.

Adult↗
PubMed2000

Thyroid hormone resistance and increased metabolic rate in the RXR-gamma-deficient mouse.

Vitamin A and retinoids affect pituitary-thyroid function through suppression of serum thyroid-stimulating hormone (TSH) levels and TSH-beta subunit gene expression. We have previously shown that retinoid X receptor-selective (RXR-selective) ligands can suppress serum TSH levels in vivo and TSH-beta promoter activity in vitro. The RXR-gamma isotype has limited tissue distribution that includes the thyrotrope cells of the anterior pituitary gland. In this study, we have performed a detailed analysis of the pituitary-thyroid function of mice lacking the gene for the RXR-gamma isotype. These mice had significantly higher serum T4 levels and TSH levels than did wild-type (WT) controls. Treatment of RXR-gamma-deficient and WT mice with T3 suppressed serum TSH and T4 levels in both groups, but RXR-gamma-deficient mice were relatively resistant to exogenous T3. RXR-gamma-deficient mice had significantly higher metabolic rates than did WT controls, suggesting that these animals have a pattern of central resistance to thyroid hormone. RXR-gamma, which is also expressed in skeletal muscle and the hypothalamus, may have a direct effect on muscle metabolism, regulation of food intake, or thyrotropin-releasing hormone levels in the hypothalamus. In conclusion, the RXR-gamma isotype appears to contribute to the regulation of serum TSH and T4 levels and to affect peripheral metabolism through regulation of the hypothalamic-pituitary-thyroid axis or through direct effects on skeletal muscle.

Animals↗
PubMed2000

Seasonal variation in lipoprotein lipase and plasma lipids in physically active, normal weight humans.

Adipose tissue lipoprotein lipase (ATLPL) provides free fatty acids (FFA) for storage in adipocytes, whereas in skeletal muscle LPL (SMLPL) provides FFA for oxidation. In hibernating animals, the level of SMLPL is relatively higher in summer than winter (promoting fat oxidation), whereas the opposite is seen with ATLPL. A patient-controlled study was designed to determine whether such seasonal variation occurs in normal weight humans. Eighteen subjects were studied in the summer and winter. After 2 days of a standardized diet, they underwent muscle and adipose biopsies for LPL activity, assessment of fitness by VO2 max, and determination of body composition by hydrostatic weighing. The percentages of body fat, body mass index, VO2 max, insulin, glucose, FFA, glycerol, and leptin were not affected by the season. Total cholesterol was higher in the winter than in the summer (157 +/- 5.5 vs. 148 +/- 4.2 mg/dL respectively; P = 0.03). The ATLPL activity was also higher in the winter than in the summer (4.4 +/- 0.8 vs. 2.3 +/- 0.6 nmol FFA/10(6) cells-min; P = 0.04). SMLPL activity trended to be higher in the winter than in the summer (1.9 +/- 0.5 vs. 1.0 +/- 0.1 nmol FFA/g x min; P = 0.06). In summary, ATLPL is seasonally regulated. It appears that SMLPL is similarly regulated by season. For physically active lean subjects, this increase in SMLPL may be a compensatory mechanism to help protect from seasonal weight gain.

Adipose Tissue↗
PubMed1999

Leptin levels in restricting and purging anorectics.

Patients with anorexia nervosa of the restricting (AN-R) and purging (AN-P) subtypes were studied to determine if there was a differential effect on leptin levels. It was hypothesized that the AN-P subgroup would have elevated leptin compared to the AN-R subgroup. Fasting plasma and anthropormorphic measurements were collected from 8 women with AN-R and 5 with AN-P. Eleven women served as controls. Overall, the plasma leptin correlated with body mass index (BMI; R = 0.432, p < .05). The AN-P subgroup had elevated leptin compared to the AN-R subgroup (3.8 +/- 0.8 vs. 1.5 +/- 0.2 ng/ml, p < .05) despite similar BMI (16.0 +/- 0.5 vs. 14.8 +/- 0.8 kg/m2). Additionally, the AN-P subgroup had similar plasma leptins as controls (3.8 +/- 0.8 vs. 3.6 +/- 0.1) despite different BMI (16.0 +/- 0.5 vs. 20.2 +/- 0.2, p < .001). Cortisol in the AN-P subgroup trended to be higher than in the restricting anorectics (21.8 +/- 3.0 vs. 15.6 +/- 1.3, p = .06). In AN, leptin was elevated in AN-P vs. AN. This may be due to increased glucocorticoid stimulation of leptin.

Adolescent↗
PubMed1999

Lipid and lipoprotein analysis of cats with lipoprotein lipase deficiency.

BACKGROUND: We have previously described a colony of domestic cats with a naturally occurring mutation in the lipoprotein lipase (LPL) gene. We have now further characterized cats homozygous for LPL deficiency (LPL -/-, homozygotes), and have contrasted these with heterozygotes (LPL +/-) and normal cats (LPL +/+). MATERIALS AND METHODS: Density gradient ultracentrifugation with subsequent lipid analysis, agarose and polyacrylamide gel electrophoresis was used to examine detailed liproprotein differences between the genotypes. Oral fat loading studies and breast milk fatty acid analysis were also performed to further characterize the phenotypic expression of LPL deficiency in this model system. RESULTS: Several lipid abnormalities associated with homozygosity for LPL deficiency were evident. Triglyceride-rich lipoprotein-triglycerides (TRL-TG) and cholesterol (TRL-C) were higher (TRL-TG 2.09 +/- 1.14 vs. 0.15 +/- 0.04 mmol L-1, P < 0.001; TRL-C 0.42 +/- 0.30 vs. 0.11 +/- 0.16 mmol L-1, P < 0.05) in male -/- than in male +/+ cats, as was HDL-cholesterol (HDL-C, 1.75 +/- 0.24 vs. 1.41 +/- 0.14 mmol L-1, P < 0.05). LDL-C levels were lower in homozygous cats than in control cats, similar to what is seen in human LPL deficiency. Oral fat loading studies revealed that homozygous cats have a marked reduced ability to clear plasma TGs in terms of peak time (7 h vs. 3 h), peak height (9.36 vs. 1.1 mmol L-1), area under the TG clearance curve (AUC, 280.3 vs. 2.2 h mmol L-1) and time to return to baseline. Fasting lipid and lipoprotein levels were not significantly different between heterozygous and normal cats. However, oral fat loading in heterozygotes revealed an intermediate phenotype (peak of 2.35 mmol L-1 at 5 h, AUC 13.1 h mmol L-1), highlighting the impaired TG clearance in these animals. CONCLUSION: Thus, LPL deficiency in the cat results in a lipid and lipoprotein phenotype that predominantly parallels human LPL deficiency, further validating the use of these animals in studies on the pathobiology of LPL.

Animals↗
PubMed1999

Plasma triglyceride reduction in mice after direct injections of muscle-specific lipoprotein lipase DNA.

The present study was conducted to determine if direct injections of plasmid pMCKhLPL DNA would lead to sufficient overexpression of lipoprotein lipase (LPL) to reduce plasma triglycerides in mice. After single intramuscular (i.m.) injections, human lipoprotein lipase (hLPL) mRNA was detectable in the quadriceps muscle for at least 21 days. Repeated intraperitoneal (i.p.) and i.m. DNA administration increased the LPL activity in skeletal muscle by 58% (i.p.) and 36% (i.m.) when compared with control-injected mice. A concomitant reduction of plasma triglycerides by 38% (i.p.) and 26% (i.m.) was obtained. Also, repeated measures of plasma triglycerides indicate that the triglyceride-lowering effect of pMCKhLPL can be noted early after DNA injections. Thus, the injection of pMCKhLPL into the peritoneum or quadriceps muscle results in plasma triglyceride reduction in mice.

Animals↗
PubMed1998

Drugs causing dyslipoproteinemia.

Diuretics and beta-blockers have a strong tendency to affect serum lipids adversely, whereas the peripherally acting alpha-blocking agents consistently result in beneficial effects. Most of the other antihypertensive agents (calcium channel blockers, ACE inhibitors, angiotensin II receptor antagonists, and drugs that act centrally) are lipid neutral. The effect of steroid hormones varies with the drug, dose, and route of administration. In general, androgens lower HDL-C and have a variable effect on LDL-C. The effects of progestins vary greatly depending on their androgenicity, and estrogens are beneficial except when hypertriglyceridemia occurs with oral estrogens. Glucocorticoids raise HDL-C and may also increase triglycerides and LDL-C. Retinoids increase triglycerides and LDL-C and also reduce HDL-C. Interferons can cause hypertriglyceridemia. Following organ transplantation, a dyslipidemia often ensues. This is caused in part by the medications used to prevent rejection (glucocorticoids, cyclosporine, and FK-506) and requires close attention and, in some patients, drug therapy to prevent coronary artery disease.

Antihypertensive Agents↗
PubMed1998

Effect of dietary macronutrient composition on tissue-specific lipoprotein lipase activity and insulin action in normal-weight subjects.

The effects of macronutrient composition on fasting and postprandial activities of adipose tissue lipoprotein lipase (ATLPL) and skeletal muscle LPL (SMLPL) and on insulin sensitivity (S(I)) were studied in 25 normal-weight subjects. Each subject was fed a high-carbohydrate (HC) diet for 16 d and a high-fat (HF) diet for 16 d, in randomized order. On day 15 of each diet, biopsies for ATLPL and SMLPL were done in the fasted state and 6 h postprandially. On day 16 of each diet, a euglycemic clamp was used to measure S(I). There was no effect of diet composition on fasting ATLPL or SMLPL. With both diets and in both tissues, LPL increased significantly from fasting to 6 h postprandially. In adipose tissue only there was a significant difference between the 2 diets in LPL meal response (HC >HF, P = 0.024). There was no effect of diet composition on S(I). After the HC diet only, there were significant correlations between fasting SMLPL and S(I), but not ATLPL. After the HF diet, associations between insulin action and LPL were evident only in the postprandial state. In summary, 16 d of HC compared with HF feeding in normal-weight subjects increased the responsiveness of ATLPL to an HC compared with an HF meal. However, the same diets had no effect on fasting ATLPL or SMLPL, the responsiveness of SMLPL to a meal, or S(I). These data suggest that in normal-weight subjects habitual dietary carbohydrate intake may have a stronger effect on subcutaneous fat storage than does dietary fat intake.

Adipose Tissue↗
PubMed1998

Abnormal oxygen uptake kinetic responses in women with type II diabetes mellitus.

Persons with type II diabetes mellitus (DM), even without cardiovascular complications have a decreased maximal oxygen consumption (VO2 max) and submaximal oxygen consumption (VO2) during graded exercise compared with healthy controls. We evaluated the hypothesis that change in the rate of VO2 in response to the onset of constant-load exercise (measured by VO2-uptake kinetics) was slowed in persons with type II DM. Ten premenopausal women with uncomplicated type II DM, 10 overweight, nondiabetic women, and 10 lean, nondiabetic women had a VO2 max test. On two separate occasions, subjects performed 7-min bouts of constant-load bicycle exercise at workloads below and above the lactate threshold to enable measurements of VO2 kinetics and heart rate kinetics (measuring rate of heart rate rise). VO2 max was reduced in subjects with type II DM compared with both lean and overweight controls (P < 0.05). Subjects with type II DM had slower VO2 and heart rate kinetics than did controls at constant workloads below the lactate threshold. The data suggest a notable abnormality in the cardiopulmonary response at the onset of exercise in people with type II DM. The findings may reflect impaired cardiac responses to exercise, although an additional defect in skeletal muscle oxygen diffusion or mitochondrial oxygen utilization is also possible.

Adult↗