Tumor necrosis factor-alpha and nitric oxide in vertically HIV-1-infected children: implications for pathogenesis

We performed a cross-sectional study to investigate the plasma TNF-alpha and nitric oxide (NO) production in 44 vertically HIV-1-infected children, and the relationship with immunological status and viral replication. As a control group, 36 healthy, uninfected children were studied. Plasma TNF-alpha and NO levels were determined by ELISA. Viral load was quantified using standard assays. Cell proliferation, apoptosis and viral replication were evaluated in vitro by incorporation of (3H)-thymidine, flow cytometry and p24 antigen, respectively. Higher plasma TNF-alpha and NO levels were observed in HIV-1-infected children compared with healthy controls. We found a very strong correlation between plasma TNF-alpha and NO levels in HIV-1-infected children (r = 0.98; p < 0.001). Moreover, HIV-1-infected children with higher viral load (> 4.7 log10) showed higher TNF-alpha and NO levels than those with viral load below this threshold. Interestingly, we detected inducible nitric oxide synthase (iNOS) mRNA in T-lymphocytes from HIV-1-infected children. To address their possible patho-physiological significance, we tested the in vitro effects of NO and TNF-alpha in HIV-1 replication. Addition of TNF-alpha and NO donors to mitogen-activated, HIV-1-infected PBMC cultures produced a significant increase in viral replication. Moreover, HIV-1 replication in mitogen-stimulated, PBMC cultures was partially inhibited by iNOS specific inhibitors, and a neutralising, anti-TNF-alpha monoclonal antibody. Our results indicate that TNF-alpha and NO correlated with high viral load in HIV-1-infected children and favoured HIV-1 in vitro replication. These data suggest a detrimental role of NO in HIV-1 infection, and that NOS inhibitors may have some therapeutic benefit in HIV-1-infection.

Regulation of human immunodeficiency virus type 1 replication in human T lymphocytes by nitric oxide

Addition of nitric oxide (NO) donors to mitogen-activated human immunodeficiency virus type 1 (HIV-1)-infected peripheral blood mononuclear cultures produced a significant increase in virus replication, and this effect was not associated with a change in cell proliferation. This effect was only observed with T-tropic X4 or X4R5 virus but not with R5 virus. Moreover, HIV-1 replication in mitogen-stimulated cultures was partially prevented by the specific inhibitors of the inducible nitric oxide synthase (iNOS). NO donors also enhanced HIV-1 infection of the human T-cell lines, Jurkat and MT-2. We have also observed that NO leads to an enhancement of HIV-1 replication in resting human T cells transfected with a plasmid carrying the entire HIV-1 genome and activated with phorbol ester plus ionomycin. Thus, in those cultures NO donors strongly potentiated HIV-1 replication in a dose-dependent manner, up to levels comparable to those with tumor necrosis factor alpha (TNF-alpha) stimulation. Furthermore, iNOS inhibitors decreased HIV-1 replication in HIV-1-transfected T cells to levels similar to those obtained with neutralizing anti-TNF-alpha antibodies. Moreover, HIV-1 replication induced iNOS and TNF-alpha transcription in T cells and T-cell lines. Interestingly, NO donors also stimulated long terminal repeat (LTR)-driven transcription whereas iNOS inhibitors partially blocked TNF-alpha-induced LTR transcription. Therefore, our results suggest that NO is involved in HIV-1 replication, especially that induced by TNF-alpha.

Induction of adhesion/differentiation of human neuroblastoma cells by tumour necrosis factor-alpha requires the expression of an inducible nitric oxide synthase

Neuroblastoma cell lines (SK-N-SH and SK-N-MC) were induced to differentiate, as detected by the expression of neurofilament proteins of 68 and 200 kDa, and to express adhesion molecules (intercellular adhesion molecule-1 and vascular cell adhesion molecule) after stimulation with tumour necrosis factor-alpha (TNF-alpha). This induction was accompanied by the arrest of cell growth. The induction of neuroblastoma adhesion by TNF-alpha could be inhibited by the nitric oxide synthase inhibitors, L-N-monomethyl arginine (L-NMMA) and L-N6-(1-imidoethyl)-lysine (highly specific for the inducible enzyme), but not by the inactive enantiomer D-NMMA. These results indicate that TNF-alpha induces the adhesion of neuroblastoma cells via nitric oxide. This was confirmed by the finding that the adhesion/differentiation of SK-N-SH and SK-N-MC cells can be directly induced by the addition of nitric oxide donors, sodium nitroprusside and S-nitroso-N-acetyl-penicillamine, into the culture medium. The isoform of the nitric oxide synthase induced in human neuroblastoma cells by TNF-alpha treatment was identified enzymatically as isoform II by Western blotting and by the polymerase chain reaction. Thus TNF-alpha induces the in vitro adhesion/differentiation of human neuroblastoma cells through nitric oxide synthesized by a calcium-independent inducible form of nitric oxide synthase, clearly indicating that isoform II of nitric oxide synthase can be expressed in human neuronal cell types.

Different phosphorylation behaviour of regulatory subunit isoforms of type II cAMP-dependent protein kinase from bovine heart

Two forms of the regulatory subunit of the type II cAMP-dependent protein kinase (RII55 and RII52) were identified from bovine heart by gel electrophoretic behaviour. After autophosphorylation the RII55 isoform migrated more slowly (RII55/57) while the migration of RII52 isoform did not shift. Both isoforms showed different affinity for cAMP. The RII55/57 isoform was eluted from a cAMP-agarose column at 10 mM cAMP at low ionic strength whereas the RII52 isoform required cAMP, plus 2M NaCl. Partial proteolysis, using trypsin or formic acid, of autophosphorylated regulatory subunit isoforms resulted in different cleavage pattern as determined by peptide mapping. However, the V8 125I-peptides patterns of both isoforms are quite similar. Incubation of partially purified holoenzyme with 10 nM [gamma-32P]ATP (low ATP concentration) yielded a single band of Mr = 57,000 which corresponds to the RII55/57 isoform. The incubation, however, at 20 microM [gamma-32P]ATP yielded two phosphobands corresponding to both RII55/57 and RII52 isoforms. The phosphorylation of RII52 took place with a lower efficiency and was more sensitive to the cAMP than the corresponding phosphorylation of the RII55/57.

Regulation of lipid metabolism by dipyridamole and adenosine antagonists in rat adipocytes

1. Acute effects of dipyridamole, an inhibitor of adenosine transport, direct activators of adenylate cyclase and thirteen adenosine antagonist analogs on fatty acid synthesis have been examined in terms of the control of [1-14C]acetate incorporation into labeled fatty acids in the presence of glucose. 2. This monosaccharide acts as a stimulator of lipogenesis by generating NADPH for the lipid synthesis. 3. The relationship between lipogenesis and lipolysis was compared with a variety of adenylate cyclase stimulators. 4. The data obtained reveals that dipyridamole potentiated the inhibitory or stimulatory effects of isoproterenol and forskolin on lipogenesis and on lipolysis, respectively. 5. In these cases the data show that it exists an inverse relationship between lipogenesis and lipolysis. 6. Dipyridamole and methylxanthine analogs only moderately affect the rate of lipolysis whereas its effects are more potent on lipogenesis and lend further support to the hypothesis that dipyridamole antagonize adenosine actions as well as methyl xanthines. 7. These results suggest that dipyridamole and adenosine antagonists alter lipogenesis independently of the lipolytic process and that it exists an inverse relationship between lipogenesis and lipolysis under some conditions whereas there are not under others.