Lipoprotein metabolism in patients with type 1 diabetes under intensive insulin treatment

Background Type 1 diabetes (T1DM) is frequently accompanied by dyslipidemia related with insulin-dependent steps of the intravascular lipoprotein metabolism. T1DM dyslipidemia may predispose to precocious cardiovascular disease and the lipid status in T1DM under intensive insulin treatment has not been sufficiently explored. The aim was to investigate the plasma lipids and the metabolism of LDL and HDL in insulin-treated T1DM patients with high glycemic levels. Methods Sixteen male patients with T1DM (26 ± 7 yrs) with glycated hemoglobin >7%, and 15 control subjects (28 ± 6 yrs) were injected with a lipid nanoemulsion (LDE) resembling LDL and labeled with 14C-cholesteryl ester and 3H-free-cholesterol for determination of fractional clearance rates (FCR, in h-1) and cholesterol esterification kinetics. Transfer of labeled lipids from LDE to HDL was assayed in vitro. Results LDL-cholesterol (83 ± 15 vs 100 ± 29 mg/dl, p=0.08) tended to be lower in T1DM than in controls; HDL-cholesterol and triglycerides were equal. LDE marker 14C-cholesteryl ester was removed faster from plasma in T1DM patients than in controls (FCR=0.059 ± 0.022 vs 0.039 ± 0.022h-1, p=0.019), which may account for their lower LDL-cholesterol levels. Cholesterol esterification kinetics and transfer of non-esterified and esterified cholesterol, phospholipids and triglycerides from LDE to HDL were also equal. Conclusion T1DM patients under intensive insulin treatment but with poor glycemic control had lower LDL-cholesterol with higher LDE plasma clearance, indicating that LDL plasma removal was even more efficient than in controls. Furthermore, HDL-cholesterol and triglycerides, cholesterol esterification and transfer of lipids to HDL, an important step in reverse cholesterol transport, were all normal. Coexistence of high glycemia levels with normal intravascular lipid metabolism may be related to differences in exogenous insulin bioavailabity and different insulin mechanisms of action on glucose and lipids. Those findings may have important implications for prevention of macrovascular disease by intensive insulin treatment.

Absorption and metabolism of volatile fatty acids by rumen and omasum

Volatile fatty acids (VFA) absorption and metabolic capacity of rumen and omasum were compared, in vitro. Fragments of rumen wall and omasum laminae were taken from eight adult crossbred bovines. An isolated fragment of the mucosa was fitted in a tissue diffusion chamber. Valeric acid and CrEDTA were added to ruminal fluid and placed on the mucosal side and buffer solution was placed on the serosal side. Fractional absorption rates were measured by exponential VFA:Cr ratio decay over time. Metabolism rate was determined as the difference between VFA absorbed and VFA which appeared on the serosal side over time. Mitotic index was higher in omasum (0.52%) than in rumen epithelium (0.28%). VFA fractional absorption rate was higher in omasum (4.6%/h.cm²) than in rumen (0.4%/h.cm²). Acetate, propionate, butyrate, and valerate showed similar fractional absorption rates in both fragments. Percentage of metabolized acetate and propionate was lower than butyrate and valerate in both stomach compartments. In the rumen, individual VFA metabolism rates were similar (mean of 7.7 , but in the omasum, valerate (90.0 was more metabolized than butyrate (59.6 propionate (69.8 and acetate (51.7 . Correlation between VFA metabolism and mitotic index was positive in the rumen and in the omasum. In conclusion, VFA metabolism and absorption potential per surface of the omasum is higher than that of the rumen. Variations on rumen and omasum absorption capacities occur in the same way, and there are indications that factors capable of stimulating rumen wall proliferation are similarly capable of stimulating omasum walls.

Metabolism of plasma cholesterol and lipoprotein parameters are related to a higher degree of insulin sensitivity in high HDL-C healthy normal weight subjects

Abstract Background We have searched if plasma high density lipoprotein-cholesterol (HDL-C) concentration interferes simultaneously with whole-body cholesterol metabolism and insulin sensitivity in normal weight healthy adult subjects. Methods We have measured the activities of several plasma components that are critically influenced by insulin and that control lipoprotein metabolism in subjects with low and high HDL-C concentrations. These parameters included cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PLTP), lecithin cholesterol acyl transferase (LCAT), post-heparin lipoprotein lipase (LPL), hepatic lipase (HL), pre-beta-1HDL, and plasma sterol markers of cholesterol synthesis and intestinal absorption. Results In the high-HDL-C group, we found lower plasma concentrations of triglycerides, alanine aminotransferase, insulin, HOMA-IR index, activities of LCAT and HL compared with the low HDL-C group; additionally, we found higher activity of LPL and pre-beta-1HDL concentration in the high-HDL-C group. There were no differences in the plasma CETP and PLTP activities. Conclusions These findings indicate that in healthy hyperalphalipoproteinemia subjects, several parameters that control the metabolism of plasma cholesterol and lipoproteins are related to a higher degree of insulin sensitivity.

Cessation of physical exercise changes metabolism and modifies the adipocyte cellularity of the periepididymal white adipose tissue in rats

All of the adaptations acquired through physical training are reversible with inactivity. Although significant reductions in maximal oxygen uptake (VO2max) can be observed within 2 to 4 wk of detraining, the consequences of detraining on the physiology of adipose tissue are poorly known. Our aim was therefore to investigate the effects of discontinuing training (physical detraining) on the metabolism and adipocyte cellularity of rat periepididymal (PE) adipose tissue. Male Wistar rats, aged 6 wk, were divided into three groups and studied for 12 wk under the following conditions: 1) trained (T) throughout the period; 2) detrained (D), trained during the first 8 wk and detrained during the remaining 4 wk; and 3) age-matched sedentary (S). Training consisted of treadmill running sessions (1 h/day, 5 days/wk, 50–60%VO2max). The PE adipocyte size analysis revealed significant differences between the groups. The adipocyte cross-sectional area (in µm2) was significantly larger in D than in the T and S groups (3,474 ± 68.8; 1,945.7 ± 45.6; 2,492.4 ± 49.08, respectively, P < 0.05). Compared with T, the isolated adipose cells (of the D rats) showed a 48% increase in the ability to perform lipogenesis (both basal and maximally insulin-stimulated) and isoproterenol-stimulated lipolysis. No changes were observed with respect to unstimulated lipolysis. A 15% reduction in the proportion of apoptotic adipocytes was observed in groups T and D compared with group S. The gene expression levels of adiponectin and PPAR-gamma were upregulated by factors of 3 and 2 in D vs. S, respectively. PREF-1 gene expression was 3-fold higher in T vs. S. From these results, we hypothesize that adipogenesis was stimulated in group D and accompanied by significant adipocyte hypertrophy and an increase in the lipogenic capacity of the adipocytes. The occurrence of apoptotic nuclei in PE fat cells was reduced in the D and T rats; these results raise the possibility that the adipose tissue changes after detraining are obesogenic.

Proline dehydrogenase regulates redox state and respiratory metabolism in Trypanosoma Cruzi

Over the past three decades, L-proline has become recognized as an important metabolite for trypanosomatids. It is involved in a number of key processes, including energy metabolism, resistance to oxidative and nutritional stress and osmoregulation. In addition, this amino acid supports critical parasite life cycle processes by acting as an energy source, thus enabling host-cell invasion by the parasite and subsequent parasite differentiation. In this paper, we demonstrate that L-proline is oxidized to Δ(1)-pyrroline-5-carboxylate (P5C) by the enzyme proline dehydrogenase (TcPRODH, E.C. 1.5.99.8) localized in Trypanosoma cruzi mitochondria. When expressed in its active form in Escherichia coli, TcPRODH exhibits a Km of 16.58±1.69 µM and a Vmax of 66±2 nmol/min mg. Furthermore, we demonstrate that TcPRODH is a FAD-dependent dimeric state protein. TcPRODH mRNA and protein expression are strongly upregulated in the intracellular epimastigote, a stage which requires an external supply of proline. In addition, when Saccharomyces cerevisiae null mutants for this gene (PUT1) were complemented with the TcPRODH gene, diminished free intracellular proline levels and an enhanced sensitivity to oxidative stress in comparison to the null mutant were observed, supporting the hypothesis that free proline accumulation constitutes a defense against oxidative imbalance. Finally, we show that proline oxidation increases cytochrome c oxidase activity in mitochondrial vesicles. Overall, these results demonstrate that TcPRODH is involved in proline-dependant cytoprotection during periods of oxidative imbalance and also shed light on the participation of proline in energy metabolism, which drives critical processes of the T. cruzi life cycle.