Liver fat and SHBG affect insulin resistance in midlife women: The Study of Women's Health Across the Nation (SWAN)

Objective:

The liver is an insulin‐responsive organ that contributes significantly to both whole body insulin sensitivity and availability of sex steroids through the production of sex hormone binding globulin (SHBG). Our objective was to explore whether lower SHBG was associated with ectopic liver fat and mediated its effect on insulin resistance in The Study of Women's Health Across the Nation (SWAN).

Design and Methods:

A subset of midlife African American and Caucasian women from SWAN (n = 208; 50.9 ± 0.18 yrs; 71% Caucasian) had computed tomography scans to quantify visceral, subcutaneous and liver fat. Blood samples were collected and assayed for hormonal and metabolic markers.

Results:

The cohort, while overweight, was generally healthy, and both liver fat and SHBG were unaffected by menopausal stage or race. Both higher liver fat and lower SHBG levels were significantly associated with higher insulin concentrations after adjustment for adiposity (r = ?0.25, P < 0.001 and r = ?0.18, P = 0.01). SHBG and liver fat had additive effects on insulin concentrations such that women with the lowest SHBG and the highest fat levels had the highest values (interaction P = 0.09). The association between SHBG and insulin was more apparent among women with fattier livers. SHBG and liver fat appear to have independent effects on insulin levels as adjustment for each other did not diminish the strength of either association (P = 0.023 and 0.001 respectively).

Conclusion:

These results confirmed the strong independent associations between increased liver fat and decreased SHBG with increased metabolic risk in midlife women. Further these data underscore the need for additional research into the role of liver fat in modifying SHBG's influence on insulin levels.

     

Passiflora plastome sequencing reveals widespread genomic rearrangements

Although past studies have included Passiflora among angiosperm lineages with highly rearranged plastid genomes (plastomes), knowledge about plastome organization in the genus is limited. So far only one draft and one complete plastome have been published. Expanded sampling of Passiflora plastomes is needed to understand the extent of the genomic rearrangement in the genus, which is also unusual in having biparental plastid inheritance and plastome‐genome incompatibility. We sequenced 15 Passiflora plastomes using either Illumina paired‐end or shotgun cloning and Sanger sequencing approaches. Assembled plastomes were annotated using Dual Organellar GenoMe Annotator (DOGMA) and tRNAscan‐SE. The Populus trichocarpa plastome was used as a reference to estimate genomic rearrangements in Passiflora by performing whole genome alignment in progressiveMauve. The phylogenetic distribution of rearrangements was plotted on the maximum likelihood tree generated from 64 plastid encoded protein genes. Inverted repeat (IR) expansion/contraction and loss of the two largest hypothetical open reading frames, ycf1 and ycf2, account for most plastome size variation, which ranges from 139 262 base pairs (bp) in P. biflora to 161 494 bp in P. pittieri. Passiflora plastomes have experienced numerous inversions, gene and intron losses along with multiple independent IR expansions and contractions resulting in a distinct organization in each of the three subgenera examined. Each Passiflora subgenus has a unique plastome structure in terms of gene content, order and size. The phylogenetic distribution of rearrangements shows that Passiflora has experienced widespread genomic changes, suggesting that such events may not be reliable phylogenetic markers.     

Effects of water-deficit on lipids of safflower aerial parts

Three-week-old plants of safflower (Carthamus tinctorius L.) were subjected to a water-deficit stress. The lipid composition of the shoot parts of both control (well-watered) and water stressed plants was analyzed. Experimental data revealed that moderate stress induced an increase in total lipid content within all lipidic classes. However, severe water-deficit induced a sharp decrease in the total lipid content and specially in polar lipids, particularly in phosphatidylethanolamine, phosphatidylcholine, monogalactosyl-diacylglycerol and digalactosyl-diacylglycerol. Also, the content of neutral lipids was increased. Concerning the fatty acid composition, water-deficit induced a decrease in their degree of unsaturation expressed by a reduction in the proportions of linolenic (18:3) and linoleic (18:2) acids and most of lipidic classes.     

Isoprostanes, prostaglandins and tocopherols in pre-eclampsia, normal pregnancy and non-pregnancy

This study is designed to evaluate whether oxidative stress and inflammation are involved in severe pre-eclampsia compared to normal pregnancy and non-pregnancy. We have measured plasma and urinary levels of 8-iso-PGF2alpha, a major isoprostane as an indicator of oxidative stress; plasma and urinary 15-keto-dihydro-PGF2alpha, a major metabolite of cyclooxygenase-catalysed PGF2alpha as an indicator of inflammatory response, and plasma -alpha-and -gamma-tocopherol in 18 pre-eclamptic, 19 normal pregnancy and 20 non-pregnant women. Pregnant women had significantly higher levels of 8-iso-PGF2alpha and PGF2alpha metabolite as compared to the non-pregnancy. Levels of 8-iso-PGF2alpha in the pre-eclamptic women did not differ from the normal pregnancy but PGF2alpha metabolite levels were significantly higher in normal pregnancy. On the other hand, gamma-tocopherol levels were significantly lower in pre-eclampsia than normal pregnancy. In contrast, the concentration of alpha-tocopherol was very similar between the groups. alpha-and gamma-tocopherol levels were significantly lower in pregnancy compared to non-pregnancy. Although no direct evidence of oxidative stress and inflammatory response was observed in severe pre-eclampsia, a reduction of gamma-tocopherol suggests the possible precedence of oxidative stress in this condition. Higher levels of isoprostanes and prostaglandin metabolite in late pregnancy suggest the importance of both free radicals and cyclooxygenase-catalysed oxidation products in normal biological processes of pregnancy.     

Lipopolysaccharide down-regulates inducible nitric oxide synthase expression in swine heart in vivo

Studies of the regulation of iNOS expression have provided many contradictory results. Comparing iNOS expression profile between cell types or organs of the same animal under the same experimental conditions may provide an explanation for these conflicting results. We have examined iNOS mRNA and protein expression in heart and liver of the same group of pigs. We found that there is a sharp difference in iNOS expression between heart and liver. The iNOS mRNA and protein was constitutively expressed in the heart at high level, but was not detectable in the liver of the same control animal. Lipopolysaccharide (LPS, 100 microg/kg, i.v.) caused a marked iNOS induction in the liver, but significantly down-regulated iNOS expression in the heart. This differential iNOS expression appears to be physiologically relevant, since LPS and the iNOS inhibitor, S-methylisothiourea, exerted different effects on hepatic and myocardial blood flow. Our data demonstrate a fundamental difference in iNOS regulation in the heart and liver of swine, and may explain the contradictory data on the regulation of iNOS expression.     

Measurement of extracellular pH,K(+), and lactate in ischemic heart

Simultaneous and continuous measurements of extracellular pH, potassium (K(+)), and lactate (L(-)) in ischemic rabbit papillary muscle are presented for the first time. Potentiometric pH and K(+) sensors and an amperometric lactate biosensor were used. These miniature electrodes were previously developed and individually tested for this purpose. The pH sensor was based on an iridium oxide layer electrodeposited on a planar platinum electrode fabricated on a flexible substrate. The potentiometric K(+) sensor was based on a polymeric membrane and valinomycin ionophore. The L(-) biosensor was based on lactate oxidase and an organic conducting salt polarized at 0.15V vs Ag/AgCl reference electrode. The utility of this novel analytical system to cardiovascular research was demonstrated by using the system to study the interrelationship of cellular K(+) and lactate loss in ischemic myocardium, and the role of extracellular pH and buffer capacity on this relationship. The results indicated: (i) sequential brief episodes of ischemia produced reproducible trends of L(-), pH, and K(+) changes during the first three episodes, (ii) extracellular L(-) increased with increasing buffer capacity of extracellular compartment, (iii) the patterns of extracellular L(-) and K(+) changes were not related directly, and (iv) L(-) transport and lactic acid diffusion were not the primary cause of extracellular acidosis during ischemia.     

The N-terminal extension of rusticyanin is not responsible for its acid stability

The N-terminal extension of rusticyanin is a unique structural feature of this protein in the cupredoxin family and has been speculated to be responsible for the extreme acid stability of the protein. We have removed the 35 residues from the N-terminus and show that the resulting -35 mutant is insoluble in aqueous media above pH 5.0 and exists primarily in a hexameric form at lower pHs. Synchrotron radiation circular dichroism (SRCD) and solution X-ray scattering data indicate that much of the beta-sheet structure is retained in acidic solution and indeed there is a small but significant increase in the beta-sheet contribution. We suggest this to be a result of beta-sheet formation between the monomer interfaces. The mutant does not bind copper. These results provide evidence that the unique N-terminus of rusticyanin is not responsible for the acid stability of the hydrophobic beta-barrel core of the protein.