Lipoprotein Lipase Overexpression in Skeletal Muscle Attenuates Weight Regain by Potentiating Energy Expenditure

Moderate weight loss improves numerous risk factors for cardiometabolic disease; however, long-term weight loss maintenance (WLM) is often thwarted by metabolic adaptations that suppress energy expenditure and facilitate weight regain. Skeletal muscle has a prominent role in energy homeostasis; therefore, we investigated the effect of WLM and weight regain on skeletal muscle in rodents. In skeletal muscle of obesity-prone rats, WLM reduced fat oxidative capacity and downregulated genes involved in fat metabolism. Interestingly, even after weight was regained, genes involved in fat metabolism were also reduced. We then subjected mice with skeletal muscle lipoprotein lipase overexpression (mCK-hLPL), which augments fat metabolism, to WLM and weight regain and found that mCK-hLPL attenuates weight regain by potentiating energy expenditure. Irrespective of genotype, weight regain suppressed dietary fat oxidation and downregulated genes involved in fat metabolism in skeletal muscle. However, mCK-hLPL mice oxidized more fat throughout weight regain and had greater expression of genes involved in fat metabolism and lower expression of genes involved in carbohydrate metabolism during WLM and regain. In summary, these results suggest that skeletal muscle fat oxidation is reduced during WLM and regain, and therapies that improve skeletal muscle fat metabolism may attenuate rapid weight regain.     

Human lymphoblastoid cells with acquired resistance to C2-desamino-C2-methyl-N10-propargyl-5,8-dideazafolic acid: a novel folate-based thymidylate synthase inhibitor.

We describe the characterization of human lymphoblastoid cell lines with acquired resistance (greater than 20,000-fold) to a novel folate-based thymidylate synthase (TS) (EC 2.1.1.45) inhibitor, C2-desamino-C2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI198583). This acquired resistance was associated with a 64-fold amplification of the TS gene, a similar elevation in the corresponding mRNA, and an approximately 200-fold increase in both TS activity and TS protein. This amplification was maintained when the cells were grown in the absence of the selective agent, ICI198583, for 340 generations. TS isolated from one of the resistant cell lines, W1-L2:C1, displayed inhibition kinetic parameters similar to those of TS isolated from the parent W1-L2 cell line. It thus appears unlikely that resistance is due to an altered TS enzyme having a lower affinity for ICI198583. The resistant cell line, W1-L2:C1, was cross-resistant to other folate-based TS inhibitors but was as sensitive as the parent cell line, W1-L2, to 5-fluorodeoxyuridine. The W1-L2:C1 cell line was collaterally sensitive to the classical dihydrofolate reductase (EC 1.5.1.3) inhibitor methotrexate as well as to the lipophilic dihydrofolate reductase inhibitors metoprine and 2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazolin e glucuronic acid salt (also called trimetrexate). When the W1-L2 and W1-L2:C1 cell lines were exposed to 1 microM ICI198583 for 24 h they accumulated the same concentration of total cellular ICI198583 polyglutamates despite the fact that the latter cell line accumulated a 300-fold greater concentration of ICI198583 monoglutamate. As polyglutamates, the tetra- and pentaglutamate forms predominated in the W1-L2 cell line, whereas the diglutamate form predominated in the W1-L2:C1 cell line, with few higher polyglutamates being detected. The lack of tri- and higher polyglutamates of ICI198583 (i.e., the more active species) in the W1-L2:C1 cell line may also contribute to the observed resistance. These findings may have important implications in light of the rapid onset of resistance to antifolates in the clinic.     

Differential forskolin activation of rat heart and lung adenylate cyclase. Dependence on membrane-protein interactions

We have investigated whether the greater ability of forskolin to activate adenylate cyclase (EC 4.6.1.1) from rat heart compared with rat lung is due to interactions between G-proteins and catalytic units, isoforms of catalytic units or membrane-protein interactions. Interactions between Gs and catalytic units were found to be similar in both tissues with 10 microM Gpp(NH)p increasing activity up to 5-fold. While MnCl2 increased the response of the lung enzyme to forskolin, it reduced the response of the cardiac enzyme and uncoupled Gs from the cardiac catalytic units indicating that Gs interactions potentiate the response to forskolin. After enzyme solubilisation with n-octyl-beta-D-glucopyranoside, the response to forskolin was identical in heart and lung whether assayed with magnesium or manganese chloride, and not significantly different from the heart membrane enzyme. Overall, the results show that the relatively poor response of lung adenylate cyclase to forskolin is due to specific inhibitory interactions between the enzyme and lung membrane constituents.     

Kinetic characteristics of ICI D1694: a quinazoline antifolate which inhibits thymidylate synthase.

The thymidylate synthase (TS) inhibitor ICI D1694 (N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N -methylamino]-2 - thenoyl)-S-glutamic acid) is a structural analogue of the substrate N5,N10-methylenetetrahydrofolate (5,10-CH2FH4) and is currently under clinical evaluation as a treatment for cancer. The compound is shown here to be a mixed non-competitive inhibitor of TS from murine leukemia (L1210) cells when 5,10-CH2FH4 is varied. This result suggests formation of an inactive complex between TS, 5,10-CH2FH4 and the inhibitor. Thus, binding to only one of the two active sites on the TS homodimer may be sufficient to prevent catalysis fully. Treatment of L1210 cells with ICI D1694 is known to cause intracellular accumulation of the tetraglutamate derivative which is shown here to have a 60-fold higher affinity for TS. The IC50 for inhibition of L1210 cell growth is below the Ki value of ICI D1694 for L1210 TS but above that of the tetraglutamate. The formation of polyglutamates and concentration of drug inside cells, therefore, seem to be responsible for biological activity.     

Computer-aided mapping of the beta-adrenoceptor. 1. Explanation for effect of para substitution on blocking activity at the beta-1-adrenoceptor.

Anomalously low affinities for the beta-1-adrenoceptor are seen for members of a series of para-substituted N-isopropylphenoxypropanolamines in which the substituent is able to conjugate with the aromatic ring. The energy of conjugation was calculated using the AM1 semiempirical molecular orbital method and appears to correlate with the loss of binding energy, and hence affinity for the receptor. This suggests that binding is associated with movement of the substituent out of the plane of the aromatic ring due to steric interference with the receptor. A previously unrecognized binding site for aromatic groups off the para position is also identified.