Identification of LRP16 as a negative regulator of insulin action and adipogenesis in 3T3-L1 adipocytes

Leukemia related protein 16 (LRP16) was first cloned from acute myeloid leukemia cells in our laboratory. In the present study, we sought to investigate the role of LRP16 in insulin action and sensitivity, using LRP16-depleted and -overexpressing 3T3-L1 cells. LRP16 silencing resulted in a reduction of the expression and secretion of tumor necrosis factor-alpha (TNF-α) and a concomitant increase in the expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ). Moreover, LRP16 depletion promoted insulin-induced glucose uptake and adipocyte differentiation of 3T3-L1 cells. In contrast, LRP16 overexpression increased TNF-α secretion, suppressed glucose uptake, and attenuated 3T3-L1 cell differentiation. The phosphorylation levels of insulin receptor substrate 1 (IRS-1), phosphatidylinositide 3-kinase (PI3-K), and Akt were increased in LRP16-deficient 3T3-L1 cells, and conversely, diminished in LRP16-overexpressing 3T3-L1 cells, when compared to the corresponding control cells. Additionally, LRP16 overexpression raised the phosphorylation level of mammalian target of rapamycin (mTOR). The pretreatment with rapamycin, a specific inhibitor of mTOR, prevented the TNF-α elevation and PPAR-γ reduction and restored the phosphorylation of IRS-1, PI3-K, and Akt in LRP16-overexpressing cells. Our data collectively indicate that LRP16 acts as a negative regulator of insulin action and adipogenesis in 3T3-L1 adipocytes, which involves the activation of the mTOR signaling pathway.

Population pharmacokinetic analysis of clopidogrel in healthy Jordanian subjects with emphasis optimal sampling strategy

AIM

Clopidogrel is metabolized primarily into an inactive carboxyl metabolite (clopidogrel-IM) or to a lesser extent an active thiol metabolite. A population pharmacokinetic (PK) model was developed using NONMEM(®) to describe the time course of clopidogrel-IM in plasma and to design a sparse-sampling strategy to predict clopidogrel-IM exposures for use in characterizing anti-platelet activity.

METHODS

Serial blood samples from 76 healthy Jordanian subjects administered a single 75 mg oral dose of clopidogrel were collected and assayed for clopidogrel-IM using reverse phase high performance liquid chromatography. A two-compartment (2-CMT) PK model with first-order absorption and elimination plus an absorption lag-time was evaluated, as well as a variation of this model designed to mimic enterohepatic recycling (EHC). Optimal PK sampling strategies (OSS) were determined using WinPOPT based upon collection of 3-12 post-dose samples.

RESULTS

A two-compartment model with EHC provided the best fit and reduced bias in C(max) (median prediction error (PE%) of 9.58% versus 12.2%) relative to the basic two-compartment model, AUC(0-24) was similar for both models (median PE% = 1.39%). The OSS for fitting the two-compartment model with EHC required the collection of seven samples (0.25, 1, 2, 4, 5, 6 and 12 h). Reasonably unbiased and precise exposures were obtained when re-fitting this model to a reduced dataset considering only these sampling times.

CONCLUSIONS

A two-compartment model considering EHC best characterized the time course of clopidogrel-IM in plasma. Use of the suggested OSS will allow for the collection of fewer PK samples when assessing clopidogrel-IM exposures.

Mast cells and the cyclooxygenase pathway mediate colonic afferent nerve sensitization in a murine colitis model

INTRODUCTION

Intestinal inflammation alters colonic afferent nerve sensitivity which may contribute to patients' perception of abdominal discomfort. We aimed to explore whether mast cells and the cyclooxygenase pathway are involved in altered afferent nerve sensitivity during colitis.

METHODS

C57Bl6 mice received 3% dextran-sulfate sodium (DSS) in drinking water for 7 days to induce colitis. Control animals received regular water. On day 8 inflammation was assessed in the proximal colon by morphology and histology. Extracellular afferent nerve discharge was recorded from the mesenteric nerve of a 2 cm colonic segment. Subgroups were treated in vitro with the mast cell stabilizer doxantrazole (10⁻⁴M) or the cyclooxygenase inhibitor naproxen (10⁻⁵M).

RESULTS

DSS colitis resulted in morphological and histological signs of inflammation. At baseline, peak firing was 11±2 imp s⁻¹ in colitis segments and 5±1 imp s⁻¹ in uninflamed control segments (p<0.05; mean ± SEM; each n=6). In colitis segments, afferent nerve discharge to bradykinin (0.5 μM) was increased to 47±7 compared to 23±6 imp s⁻¹ in recordings from non-inflamed control tissue (p<0.05). Mechanosensitivity during luminal ramp distension (0-80 cm H₂O) was increased reaching 24±5 imp s⁻¹ at 80 cm H₂O during colitis compared to 14±2 in non-inflamed controls (p<0.05). Doxantrazole or naproxen reduced afferent discharge to bradykinin and luminal ramp distension in colitis segments to control levels.

CONCLUSION

Intestinal inflammation sensitizes mesenteric afferent nerve fibers to bradykinin and mechanical stimuli. The underlying mechanism responsible for this sensitization seems to involve mast cells and prostaglandins.

Development of a new model of transvenous thrombosis in the pig superior sagittal sinus using thrombin injection and balloon occlusion

PURPOSE

To establish an experimental model of superior sagittal sinus (SSS) thrombosis using a transvenous route, and thrombin and balloon occlusion, in pigs.

METHODS

The SSS was catheterized transvenously in six pigs. Thrombin was injected into the pigs' SSS to induce thrombosis. Magnetic resonance imaging (MRI) and magnetic resonance venography (MRV) confirmed successful SSS thrombosis. MRI and MRV were also used to observe the evolution of thrombus and accompanying brain parenchymal changes before thrombus induction postoperatively on Days 1, 3, and 7. The pigs were sacrificed for histological examination at the follow-up.

RESULTS

SSS thrombosis was successfully achieved in all six pigs. On Day 1 postoperatively, MRV confirmed SSS thrombosis and MRI revealed brain edema in each animal. On Day 3, venous infarction was noted in two cases, one of which appeared to be hemorrhagic. On Day 7, MRV showed partial recanalization of the SSS in one pig. Brain edema was significantly relieved in four cases while, in two other cases, the extent of venous infarction was reduced. Histological examination confirmed SSS thrombosis in all animals, with recanalization in only one case. In two of the animals, bilateral parasagittal infarction was seen, including one with petechial hemorrhage. In the other four animals, bilateral parasagittal edema was observed.

CONCLUSION

The development of an experimental model of SSS via the transvenous route is feasible in pigs using thrombin and balloon occlusion. This model closely resembles SSS thrombosis in humans, and can be applied in the clinical study of this phenomenon as well as in clinical therapeutic applications.

Afferent nerve sensitivity is decreased by an iNOS-dependent mechanism during indomethacin-induced inflammation in the murine jejunum in vitro

Evidence exists that visceral afferent sensitivity is subject to regulatory mechanisms. We hypothesized that afferent sensitivity is decreased in the small intestine during intestinal inflammation by an inducible nitric oxide synthase (iNOS)-dependent mechanism. C57BL/6 mice were injected twice with vehicle or 60 mg kg(-1) indomethacin subcutaneously to induce intestinal inflammation. Afferent sensitivity was recorded on day 3 from a 2-cm segment of jejunum in vitro by extracellular multi-unit afferent recordings from the mesenteric nerve bundle. In subgroups (n = 6), iNOS was inhibited selectively by L-N6-(1-iminoethyl)-lysine (L-NIL) given either chronically from day 1-3 (3 mg kg(-1) twice daily i.p.) or acutely into the organ bath (30 micromol L(-1)). The indomethacin-induced increase of macroscopic and microscopic scores of intestinal inflammation (both P < 0.05) were unchanged after pretreatment with L-NIL. Peak afferent firing following bradykinin (0.5 micromol L(-1)) was 55 +/- 8 impulse s(-1) during inflammation vs 97 +/- 7 impulse s(-1) in controls (P < 0.05). Normal firing rate was preserved following L-NIL pretreatment (112 +/- 16 impulse s(-1)) or acute administration of L-NIL (108 +/- 14 impulse s(-1)). A similar L-NIL dependent reduction was observed for 5-HT (250 micromol L(-1)) and mechanical ramp distension from 20 to 60 cmH(2)O (both P < 0.05). Intraluminal pressure peaks were decreased to 0.66 +/- 0.1 cmH(2)O during inflammation compared to 2.51 +/- 0.3 in controls (P < 0.01). Afferent sensitivity is decreased by an iNOS-dependent mechanism during intestinal inflammation which appears to be independent of the inflammatory response. This suggests that iNOS-dependent nitric oxide production alters afferent sensitivity during inflammation by interfering with signal transduction to afferent nerves rather than by attenuating intestinal inflammation.

Effect of total flavonoid fraction of Astragalus complanatus R. Brown on angiotensin II-induced portal-vein contraction in hypertensive rats

The objective of the present study was to examine further the underlying mechanism of the antihypertensive effect of the total flavonoid (TF), extracted from the seed of Astragalus complanatus R.Brown. Renovascular hypertension rats (RHR) were established by the two-kidney one clip (2K1C) method. The effect of TF on the contraction of portal vein was studied in an isolated preparation. The response of portal vein to angiotensin II (Ang II) was expressed as a percentage of the 100 mmol/l KCl induced maximum contraction. We took the dose-response curve of portal vein to Ang II (from 10(-9) to 10(-6) mmol/l) as the control and then observed the change of curve after TF and Valsartan (Ang II receptor blocker) administration. Ang II induced a concentration-dependent increase of the contraction amplitude (maximal increase, 46.53+/-5.15% of 100 mmol/l KCl induced contraction at Ang II 10(-6) mmol/l in RHR). The Ang II-induced portal vein contraction was prevented by TF with a concentration related manner (maximal inhibition amplitude from 46.53+/-5.15% to 22.525+/-4.67% of 100 mmol/l KCl contraction at 10(-6)mmol/l Ang II and 3.12 x 10(-1) mg/l TF in RHR). The effect of TF on Ang II-induced portal vein contraction was similar to Valsartan. These results showed that the antihypertensive action of TF was attributed to the dilation of vessels and is related to the blockade of the Ang II receptor.

Sex differences in angiotensin II- induced hypertension

Sex differences in the development of hypertension and cardiovascular disease have been described in humans and in animal models. In this paper we will review some of our studies which have as their emphasis the examination of the role of sex differences and sex steroids in modulating the central actions of angiotensin II (ANG II) via interactions with free radicals and nitric oxide, generating pathways within brain circumventricular organs and in central sympathomodulatory systems. Our studies indicate that low-dose infusions of ANG II result in hypertension in wild-type male mice but not in intact wild-type females. Furthermore, we have demonstrated that ANG II-induced hypertension in males is blocked by central infusions of the androgen receptor antagonist, flutamide, and by central infusions of the superoxide dismutase mimetic, tempol. We have also found that, in comparison to females, males show greater levels of intracellular reactive oxygen species in circumventricular organ neurons following long-term ANG II infusions. In female mice, ovariectomy, central blockade of estrogen receptors or total knockout of estrogen a receptors augments the pressor effects of ANG II. Finally, in females but not in males, central blockade of nitric oxide synthase increases the pressor effects of ANG II. Taken together, these results suggest that sex differences and estrogen and testosterone play important roles in the development of ANG II-induced hypertension.

Protective effect of glutathione against lipopolysaccharide-induced inflammation and mortality in rats

OBJECTIVE

To investigate protective effect of glutathione (GSH) against lipopolysaccharide (LPS)-induced inflammation and mortality in rats.

METHODS

Male Sprague-Dawley rats were injected intraperitoneally (i. p.) with GSH (40 mg/kg) 30 min prior to LPS injection (20 mg/kg). Animal survival rate and the production of nitric oxide in serum were measured. Morphology of lung was observed using hematoxylin and eosin staining. Western blotting was used to assess the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and the phosphorylation of p38 in rat peritoneal macrophages.

RESULTS

GSH significantly decreased LPS-induced mortality, inhibited serum NO production and eliminated lung histological injury. Furthermore, GSH inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins and the phosphorylation of p38 in LPS-stimulated rat peritoneal macrophages.

CONCLUSIONS

These results indicated that GSH suppressed LPS-induced systemic inflammatory response in rats and p38 MAPK signal pathway was involved in this process.

Seasonal changes in weight and body composition of yak grazing on alpine-meadow grassland in the Qinghai-Tibetan plateau of China

Forty-five male yaks (born April 2001) were studied to determine how seasonal changes on the Qinghai-Tibetan plateau affected BW and body composition. Thirty yaks were weighed monthly from birth to 26 mo of age to determine seasonal changes in BW. The remaining 15 yaks were allocated randomly to five groups (three yaks per group), designated for slaughter at 13, 15, 18, 22, and 25 mo to measure seasonal effects on body chemical composition. All yaks were grazed on the alpine-meadow grassland of the plateau without any supplementation. All BW and body composition data were calculated on an individual basis. Body weight and body composition data were both compared across seven growth periods spanning 2 yr and defined by season. From April (birth) to December 2001 of the first growing season, yak BW increased (P < 0.01); however, during the subsequent cold season (December 2001 to May 2002), BW decreased (P < 0.01). The second growing season ran from May 2002 (13 mo of age) to October 2002 (18 mo of age), and the second live weight-loss season ran from October 2002 until May 2003. The weight loss experienced by yaks during the first weight-loss season was 25.64% of the total weight gain in the first growing season. The weight loss experienced by yaks during the second weight-loss season was 29.73% of the total weight gain in the second growing season. Energy retention in the second growing season was 291.07 MJ, 50.8% of which was consumed during the subsequent cold season. Energy accumulation in the summer (from May to July) and fall (from July to October) of the second growing season did not differ (5.01 and 6.30 MJ/kg of EBW gain, respectively; P = 0.63). The energy mobilized during the second winter (from October 2002 to February 2003) was 16.49 MJ/kg of EBW, and in the second spring (from February to May 2003), it was 9.06 MJ/kg of EBW. These data suggest that the decrease in grazing yak BW during the first cold season is much less than during the second cold season, and that the energy content per unit of BW mobilized is greater (P = 0.02) in winter than in spring. Results from this study demonstrate highly efficient compensatory growth in grazing yaks following the first weight loss period during the first cold season. This benefit could be exploited by herders to improve yak production. Yaks may have developed a type of self-protection mechanism to overcome the long cold seasons in the Qinghai-Tibetan plateau.

Human glutathione S-transferase P1-1 interacts with TRAF2 and regulates TRAF2-ASK1 signals

Human glutathione S-transferase P1-1 (GSTP1-1) is an ubiquitously expressed protein that plays an important role in the detoxification and xenobiotics metabolism. It has been shown that GSTP1-1 interacts with c-Jun NH(2)-terminal kinase (JNK) and suppresses its activity. Here, we report a novel function of GSTP1-1 in regulating tumor necrosis factor-alpha (TNF-alpha)-triggered signaling. The present experiments showed that GSTP1-1 physically associated with tumor necrosis factor receptor-associated factor 2 (TRAF2) in vivo and in vitro. Overexpression of GSTP1-1 inhibited TRAF2-induced activation of both JNK and p38 but not of nuclear factor-kappaB (NF-kappaB). Glutathione S-transferase P1-1 also attenuated TRAF2-enhanced apoptosis signal-regulating kinase 1 (ASK1) autophosphorylation and inhibited TRAF2-ASK1-induced cell apoptosis by suppressing the interaction of TRAF2 and ASK1. Conversely, silencing of GSTP1-1 expression through RNA interference (RNAi) resulted in increase of TNF-alpha-dependent TRAF2-ASK1 association followed by hyper-activation of ASK1 and JNK. A mutant GSTP1-1 lacking TRAF domain-binding motif exhibited a significant decline of capacity to bind TRAF2 and block TRAF2-ASK1 signaling compared with the wild type of GSTP1-1. Moreover, the glutathione-conjugating activity of GSTP1-1 was not involved in the regulation of TRAF2 signaling. These findings indicate that GSTP1-1 plays an important regulatory role in TNF-alpha-induced signaling by forming ligand-binding interactions with TRAF2, which provides a new insight for analysing the protective effects of GSTP1-1 in tumor cells.

Characterization of a MYBR2R3 gene from black spruce (Picea mariana) that shares functional conservation with maize C1

PCR amplification with degenerate primers targeted to highly conserved amino acid motifs within the MYB domain was used to demonstrate that black spruce (Picea mariana) possesses a diverse MYB gene family. Amino acid sequence comparisons revealed three broad MYB subfamilies, one of which shares extensive similarity with maize C1, a central regulator of anthocyanin biosynthesis. A cDNA clone encoding a MYBR2R3 protein from P. mariana with high levels of sequence homology to maize C1 was shown to transactivate the Bz2 promoter in combination with maize R in embryonal tissues of both black spruce and larch. Functional dependence on the maize R protein, and the presence of a conserved C-terminal GIDPxTH motif, support the conservation of MYBR2R3 function in conifers, and demonstrate that the basic components of MYBR2R3-dependent transcriptional regulation have been conserved between angiosperms and gymnosperms.

Mechanism of intracellular calcium ([Ca2+]i) inhibition of lipolysis in human adipocytes

We investigated the mechanisms responsible for the anti-lipolytic effect of intracellular Ca2+ ([Ca2+]i) in human adipocytes. Increasing [Ca2+]i inhibited lipolysis induced by b-adrenergic receptor activation, A1 adenosine receptor inhibition, adenylate cyclase activation, and phosphodiesterase (PDE) inhibition, as well as by a hydrolyzable cAMP analog, but not by a nonhydrolyzable cAMP analog. This finding indicates that the anti-lipolytic effect of [Ca2+]i may be mediated by the activation of adipocyte PDE. Consistent with this theory, [Ca2+]i inhibition of isoproterenol-stimulated lipolysis was reversed completely by the nonselective PDE inhibitor isobutyl methylxanthine and also by the selective PDE 3B inhibitor cilostamide, but not by selective PDE 1 and 4 inhibitors. In addition, phosphatidylinositol-3 kinase inhibition with wortmannin completely prevented insulin's anti-lipolytic effect but only minimally blocked [Ca2+]i's effect, which suggests that [Ca2+]i and insulin may activate PDE 3B via different mechanisms. In contrast, the antilipolytic effect of [Ca2+]i was not affected by inhibitors of calmodulin, Ca2+/calmodulin-dependent kinase, protein phosphatase 2B, and protein kinase C. Finally, [Ca2+]i inhibited significantly isoproterenol-stimulated increases in cAMP levels and hormone-sensitive lipase phosphorylation in human adipocytes. In conclusion, increasing [Ca2+]i exerts an antilipolytic effect mainly by activation of PDE, leading to a decrease in cAMP and HSL phosphorylation and, consequently, inhibition of lipolysis.

Enhancing protein capacity of rigid macroporous polymeric adsorbent

A macroporous poly(glycidyl methacrylate-triallyl isocyanurate-divinylbenzene) resin was synthesized and modified with diethylamine to yield an anion-exchange resin suitable for protein adsorption. Efforts were made to enhance protein ion exchange capacity of the resin by investigating the copolymer composition. Different synthesis recipes were attempted, and the resultant resins were characterized by measuring the specific surface area and the adsorption ability using bovine serum albumin (BSA) as a model protein. The intraparticle pore size distribution measured by mercury porosimetry showed that the pores in the range of 40-120 nm took 75% of the total pore volume, indicating that the ion exchanger was favorable for protein adsorption. BSA capacity obtained with an appropriate recipe was as high as 78.6 mg/g wet resin or 50 mg/mL packed volume, which was higher than the capacities of some commercially available ion exchangers. Moreover, by using a pore diffusion model, the effective pore diffusivity of BSA was found to be 5.5 x 10(-12) m(2)/s, similar to those in the commercial ion exchangers.