Regulation of intestinal apolipoprotein A-IV synthesis

Abstract Apolipoprotein (apo) A-IV is a protein synthesized, in humans, only by the small intestine. It has a molecular weight of 46 000 Da. This paper summarizes the evidence supporting its role as a satiety factor following the ingestion of fat. This function of apo A-IV is unique and not shared by other apolipoproteins, including apo A-I. The satiety effect of apo A-IV is centrally mediated. The mechanism of how apo A-IV inhibits food intake is not clear but it probably acts by inhibiting both gastric acid secretion as well as gastric motility. Lipid absorption stimulates apo A-IV synthesis and secretion by the jejunum. In addition to lipid feeding, there is evidence that a factor which is released as a result of lipid absorption in the distal small intestine also stimulates the synthesis and release of apo A-IV by the jejunum. This factor is probably PYY.     

Haplotype and interspersion analysis of the FMR1 CGG repeat identifies two different mutational pathways for the origin of the fragile X syndrome

To understand the origins of the fragile X syndrome and factors predisposing alleles to instability and hyperexpansion, we have compared the haplotype (using markers FRAXAC1, FRAXAC2, and DXS548) and AGG interspersion patterns of the FMR1 CGG repeat for 214 normal and 16 premutation chromosomes. Association testing between interspersion pattern and haplotype reveals a highly significant (P < 0.002) non- random distribution, indicating that all three markers are useful in phylogenetic reconstruction of mutational change. Parsimony analysis of the FMR1 CGG repeat substructure predicts that loss of AGG interruptions has occurred independently on many haplotypes associated with the fragile X syndrome, partially explaining the haplotype diversity of this disease. Among haplotypes found in linkage disequilibrium with the fragile X mutation, two different modes of mutation and predisposition to instability have been identified. One pathway has involved the frequent and recurrent loss of AGG interruptions from rare asymmetrical ancestral array structures. Intergenerational transmission studies suggest that these predisposed chromosomes progress relatively rapidly to the disease state. In contrast, the second mutational pathway involves a single haplotype which has maintained two AGG interruptions. Parsimony analysis of CGG repeat substructure within this haplotype suggests that larger alleles have been generated by gradual increments of CGG repeats distal to the most 3' interruption. Pedigree analysis of the intergenerational stability of alleles of this haplotype confirms a gradual progression toward instability thresholds. As a result, a large reservoir of chromosomes carrying large repeats on this haplotype exists. These chromosomes are predisposed to disease. The present data support a model in which there are at least two different mutational pathways predisposing alleles to instability and hyperexpansion associated with the fragile X syndrome.      

Leukaemia inhibitory factor expression in human follicular fluid and ovarian cells

Leukaemia inhibitory factor (LIF) is a 43 kDa glycoprotein with a remarkable range of biological actions in different tissue systems. LIF improves the rate of fertilization of mouse oocytes in vitro and up- regulates aromatase enzyme. We postulated that LIF may be an important modulator of ovarian function and may also improve embryo quality in humans. Follicular fluid samples from patients undergoing in-vitro fertilization (IVF) and embryo transfer (n = 123), from women undergoing ovarian stimulation (n = 4) and from women undergoing laparoscopy for tubal ligation during their follicular phase (n = 3) were used. Follicular fluid LIF, oestradiol, and progesterone were measured and embryo quality was assessed. Granulosa-lutein cells were cultured for 3 days in Ham's F-12:Dulbecco's modified Eagle's medium (DMEM). Ovarian stromal cells, isolated by enzymatic dispersion of ovarian tissue, were also cultured in the same medium. Following experimental treatments, LIF mRNA and protein concentrations were quantified. The concentration of LIF was 0.8 +/- 0.3 (mean +/- SEM) pg/ml in pre-human chorionic gonadotrophin (HCG) follicular fluid samples and 13.0 +/- 1.1 pg/ml in post-HCG follicular fluid samples (P < 0.05). LIF levels were undetectable in three follicular fluid samples obtained during unstimulated follicular phase. There was a correlation between follicular fluid LIF and follicular fluid oestradiol concentrations (r = 0.36; P = 0.0001) and the number of grade I embryos (r = 0.62; P = 0.01). LIF mRNA and the protein were expressed constitutively but in low amounts in the ovarian stromal cell cultures. The concentrations of LIF mRNA as well as protein were increased by interleukin (IL)-1alpha and tumour necrosis factor alpha (TNF alpha) in a time- and concentration-dependent manner. Purified granulosa-lutein cells expressed low amounts of LIF mRNA and protein which were not significantly increased by IL-1alpha or TNF alpha. Our findings suggest that HCG stimulates the expression of LIF in follicular fluid. Both granulosa-lutein and ovarian stromal cells express the LIF mRNA and produce the protein. Modulation of LIF in these cells may play an important role in the physiology of ovulation and early embryo development.      

Preliminary In Vitro Antisickilng Properties of Crude Juice Extracts of Persia Americana,Citrus Sinensis,Carica Papaya and Ciklavit?

The antisickling properties of crude juice extracts of the edible portions of three commonly consumed tropical fruits namely Persia americana, Citrus sinensis, and Carica papaya were investigated in vitro alongside a new drug preparation called Ciklavit® that has antisickling activity. Four different solvent extracts of the crude juice of each fruit including aqueous, acidic, alkaline and alcoholic extracts were prepared and their antisickling effects on sickle cell trait (HbAS) and sickle cell disease (HbSS) blood samples checked alongside Ciklavit®. Blood samples were stabilized using normal saline and the antisickling effects were checked by counting the number of sickle cells remaining after incubation of the blood samples with the crude fruit extracts and Ciklavit® for twenty-four hours. The results showed that Ciklavit® produced a sustained reduction in the number of sickle cells in both HbAS and HbSS blood samples. Also the alkaline and alcoholic extracts of P. americana and C. papaya produced significant reduction in the number of sickle cells.     

The vascular effects of different arginase inhibitors in rat isolated aorta and mesenteric arteries

Background and purpose

Arginase and nitric oxide (NO) synthase share the common substrate L-arginine, and arginase inhibition is proposed to increase NO production by increasing intracellular levels of L-arginine. Many different inhibitors are used, and here we have examined the effects of these inhibitors on vascular tissue.

Experimental approach

Each arginase inhibitor was assessed by its effects on isolated rings of aorta and mesenteric arteries from rats by: (i) their ability to preserve the tolerance to repeated applications of the endothelium-dependent agonist acetylcholine (ACh); and (ii) their direct vasorelaxant effect.

Key results

In both vessel types, tolerance (defined as a reduced response upon second application) to ACh was reversed with addition of L-arginine, (S)-(2-boronethyl)-L-cysteine HCl (BEC) or N^G-Hydroxy-L-arginine (L-NOHA). On the other hand, N^ω-hydroxy-nor-L-arginine (nor-NOHA) significantly augmented the response to ACh, an effect that was partially reversed with L-arginine. No effect on tolerance to ACh was observed with L-valine, nor-valine or D,L, α-difluoromethylornithine (DFMO). BEC, L-NOHA and nor-NOHA elicited endothelium-independent vasorelaxation in both endothelium intact and denuded aorta while L-valine, DFMO and nor-valine did not.

Conclusions and implications

BEC and L-NOHA, but not nor-NOHA, L-valine, DFMO or nor-valine, significantly reversed tolerance to ACh possibly conserving L-arginine levels and therefore increasing NO bioavailability. However, both BEC and L-NOHA caused endothelium-independent vasorelaxation in rat aorta, suggesting that these inhibitors have a role beyond arginase inhibition alone. Our data thus questions the interpretation of many studies using these antagonists as specific arginase inhibitors in the vasculature, without verification with other methods.     

Relation between regional and global systolic function in patients with ischemic cardiomyopathy after β-Blocker therapy or revascularization

Background

To assess the relationship between improved regional and global myocardial function in patients with ischemic cardiomyopathy in response to β-blocker therapy or revascularization.

Materials and methods

Cardiovascular Magnetic Resonance (CMR) was performed in 32 patients with ischemic cardiomyopathy before and 8 ± 2 months after therapy. Patients were assigned clinically to β-blocker therapy (n = 20) or revascularization (n = 12). CMR at baseline was performed to assess regional and global LV function at rest and under low-dose dobutamine. Wall thickening was analyzed in dysfunctional, adjacent, and remote segments. Follow-up CMR included rest function evaluation.

Results

Augmentation of wall thickening during dobutamine at baseline was similar in dysfunctional, adjacent and remote segments in both patient groups. Therefore, baseline characteristics were similar for both patient groups. In both patient groups resting LV ejection fraction and end-systolic volume improved significantly (p < 0.05) at follow-up. Stepwise multivariate analysis revealed that improvement in global LV ejection fraction in the β-blocker treated patients was significantly related to improved function of remote myocardium (p < 0.05), whereas in the revascularized patients improved function in dysfunctional and adjacent segments was more pronounced (p < 0.05).

Conclusion

In patients with chronic ischemic LV dysfunction, β-Blocker therapy or revascularization resulted in a similar improvement of global systolic LV function. However, after β-blocker therapy, improved global systolic function was mainly related to improved contraction of remote myocardium, whereas after revascularization the dysfunctional and adjacent regions contributed predominantly to the improved global systolic function.     

Effect of platelet-activating factor (PAF) on human platelets

The effect of pure synthetic PAF (1-0-alkyl-2-acetyl-sn-glycero-3- phosphorylcholine) was studied in human platelets. PAF (0.2--2.0 micrograms/ml) produced a dose-dependent aggregation in human platelet- rich plasma (PRP) or platelet suspension obtained by gel-filtration (GFP). In addition, PAF (0.8 microgram/ml) induced secretion of 14C- serotonin (45% +/- 10%; mean +/- SD, n = 9) and platelet factor 4 (PF4) (12.89 +/- 3.81 micrograms/10(9) platelets; n = 9) in PRP. Similar results were obtained in GFP. Aggregation and release of 14C-serotonin and PF4 were inhibited by the metabolic inhibitors 2-deoxyglucose (16.7 mM) and antimycin-A (8.3 micrograms/ml), by the membrane-active drugs mepacrine (10 microM) and chlorpromazine (0.025 mM), by PGI2 (5.34 nM), which elevates intracellular c-AMP, by indomethacin (10 microM) or aspirin (100 microM). The ADP scavengers, creatine phosphate and creatine phosphokinase (CP/CPK), inhibited the second wave of aggregation but not secretion. These data suggest that the major effect of PAF on human platelets is mediated through the cyclo-oxygenase pathway and not through a third pathway.