Joan Carles Domingo

Human dendritic cell activities are modulated by the omega-3 fatty acid, docosahexaenoic acid, mainly through PPARγ:RXR heterodimers: comparison with other polyunsaturated fatty acids

There is accumulating evidence that omega‐3 fatty acids may modulate immune responses. When monocytes were differentiated to dendritic cells (DCs) in the presence of docosahexaenoic acid (DHA), the expression of costimulatory and antigen presentation markers was altered in a concentration‐dependent way, positively or negatively, depending on the markers tested and the maturation stage of the DCs. Changes induced by eicosapentaenoic acid and linoleic acid were similar but less intense than those of DHA, whereas oleic acid had almost no effect. DHA‐treated, mature DCs showed inhibition of IL‐6 expression and IL‐10 and IL‐12 secretion, and their lymphoproliferative stimulation capacity was impaired. The phenotypic alterations of DCs induced by DHA were similar to those already reported for Rosiglitazone (Rosi), a peroxisome proliferator‐activated receptor γ (PPARγ) activator, and the retinoid 9‐cis‐retinoic acid (9cRA), a retinoid X receptor (RXR) activator. Moreover, DHA induced the expression of PPARγ target genes pyruvate dehydrogenase kinase‐4 and aP‐2 in immature DCs. The combination of DHA with Rosi or 9cRA produced additive effects. Furthermore, when DCs were cultured in the presence of a specific PPARγ inhibitor, all of the changes induced by DHA were blocked. Together, these results strongly suggest that the PPARγ:RXR heterodimer is the pathway component activated by DHA to induce its immunomodulatory effect on DCs.

Targeting nanoparticles to dendritic cells for immunotherapy.

Dendritic cells (DCs) are key players in the initiation of adaptive immune responses and are currently exploited in immunotherapy for treatment of cancer and infectious diseases. Development of targeted nanodelivery systems carrying vaccine components, including antigens and adjuvants, to DCs in vivo represents a promising strategy to enhance immune responses. Delivering particulate vaccines specifically to DCs and preventing nonspecific uptake by other endocytotic cells are challenging. Size represents a critical parameter determining whether particulate vaccines can penetrate lymph nodes and reach resident DCs. Specific delivery is further enhanced by actively targeting DC-specific receptors. This chapter discusses the rationale for the use of particle-based vaccines and provides an overview of antigen-delivery vehicles currently under investigation. In addition, we discuss how vaccine delivery systems may be developed, focusing on liposomes, PLGA polymers, and gold nanoparticles, to obtain safe and efficacious vaccines.

Switching to Nevirapine Decreases Insulin Levels but Does Not Improve Subcutaneous Adipocyte Apoptosis in Patients with Highly Active Antiretroviral Therapy–Associated Lipodystrophy

Subcutaneous adipocyte apoptosis occurs in lipotrophic areas of patients with highly active antiretroviral therapy (HAART)-associated lipodystrophy. Fourteen patients with HAART-associated lipodystrophy had 2 subcutaneous biopsies for evidence of adipocyte apoptosis, the second after a randomized change to nevirapine (n=8) or after remaining on a regimen of indinavir-based HAART (n=6). Apoptosis was assessed by the terminal deoxynucleotidyl transferase dUTP-digoxigenin nick end-labeling method. Patients who were switched to nevirapine had a significant decrease in insulinemia and a significant increase in the glucose:insulin ratio. Overall, subcutaneous adipocyte apoptosis increased in 3 patients who were switched to nevirapine and in 3 who continued to receive indinavir but decreased in 2 patients switched to nevirapine and another 2 who continued to receive indinavir. Subcutaneous adipocyte apoptosis continues to occur in lipotrophic areas of patients with HAART-associated lipodystrophy despite switching from indinavir to nevirapine, suggesting that such a strategy will be useless for reversal of lipoatrophy.

In Vitro Cytotoxicity and Mitochondrial Toxicity of Tenofovir Alone and in Combination with Other Antiretrovirals in Human Renal Proximal Tubule Cells

ABSTRACT We assessed the in vitro toxicity of tenofovir (TFV) and compared it with those of zidovudine (AZT), didanosine (ddI), ritonavir (RTV), and lopinavir (LPV) alone and in combination in human renal proximal tubule epithelial cells (RPTECs). The cells were treated with various concentrations and combinations of the tested antiretrovirals for up to 22 days, and cytotoxicity was determined. In addition, we assessed the levels of mitochondrial DNA (mtDNA) and cytochrome oxidase II (COII) mRNA in RPTECs treated with reverse transcriptase inhibitors. TFV alone was not associated with significant cytotoxicity. ddI showed pronounced cytotoxicity that was greater than those of AZT (P = 0.002) and TFV (P = 0.0001). The combination of 10 μM RTV and 40 μM LPV significantly reduced RPTEC viability (P < 0.0001), and TFV tended to partially reduce this effect. TFV alone affected neither mtDNA nor COII mRNA levels, whereas ddI caused a profound depletion of mtDNA and a parallel reduction in COII mRNA expression. The effects of ddI, but not those of AZT, on mtDNA and COII mRNA were further enhanced in the presence of TFV, a finding consistent with the inhibition of ddI clearance by TFV. The addition of TFV to ddI or AZT appeared to slightly increase the COII mRNA/mtDNA ratio relative to that in cells treated with ddI or AZT alone. Together, these in vitro results indicate that combination with other antiretrovirals does not significantly increase the toxic potential of TFV in RPTECs.

Targeting nanosystems to human DCs via Fc receptor as an effective strategy to deliver antigen for immunotherapy.

Dendritic cells (DCs) are increasingly being explored as cellular vaccines for tumor immunotherapy, since they provide an effective system of antigen presentation both in vitro and in vivo. An additional advantage of this cell type is that it is possible to target specific antigens through the activation of receptors, such as FcR (the receptor for the IgG Fc fragment) and TLR (toll-like Receptor). Thus, the uptake capacity of DCs can be improved, thereby increasing antigen presentation. This, in turn, would lead to an enhanced immune response, and, in some instances, the tolerance/anergy of immune effector cells present in cancer patients could be reverted. Here we studied various nanotargeting systems, including liposomes and gold nanoparticles of a peptide-based immunotherapeutic vaccine for the treatment of androgen-responsive prostate cancer. Building blocks of the immunogenic peptide consisted of the luteinizing hormone-releasing hormone (LHRH), also known as gonadotropin-releasing hormone (GnRH) peptide (B- and T-cell epitope), in tandem with a T-helper epitope corresponding to the 830-844 region of tetanus toxoid. Three new peptides with several modifications at the N-terminal (palmitoyl, acetyl, and FITC) were synthesized. These peptides also contained a Cys as C-terminal residue to facilitate grafting onto gold nanoparticles. To target different antigen formulations to human DCs, the Fc was activated with a cross-linking spacer to generate a free thiol group and thus facilitate conjugation onto gold nanoparticles, liposomes, and peptide. Our results show that gold nanoparticles and liposomes targeted to FcRs of human DCs are effective antigen delivery carriers and induce a strong immune response with respect to nontargeted LHRH-TT-nanoparticle conjugates and a superior response to that of naked antigens. In addition, dual labeling using gold and FITC-peptide allowed DC tracking by flow cytometry as well as transmission electron microscopy. Nanoparticles were observed to show a homogeneous distribution throughout the cytoplasm. These results open up a new approach to the development of a novel strategy for cancer vaccines.

N-PALMITOYLPHOSPHATIDYLETHANOLAMINE STABILIZES LIPOSOMES IN THE PRESENCE OF HUMAN SERUM : EFFECT OF LIPIDIC COMPOSITION AND SYSTEM CHARACTERIZATION

Liposomes containing negatively-charged phospholipid, N-palmitoylphosphatidylethanolamine (NPPE) were examined for stability in the presence of human serum, using the release of the entrapped 5,6-carboxyfluorescein as an aqueous marker. Either small unilamellar vesicles (SUV) or large unilamellar vesicles (LUV) were used. Incorporation of NPPE into PC SUV decreases leakage in the presence of serum or phosphate-buffered saline, no strictly related to size increase observed and to the surface negative charge present. The stabilizing effect of NPPE and Chol were synergistic. Inhibition of destabilization induced by serum of PC/Chol liposomes was observed when NPPE concentrations were above 12 mol%. Change in the membrane fluidity or incorporation of a monosialoganglioside into liposomes do not significantly change the half-life of liposomes in the presence of a high NPPE concentration. Incorporation of NPPE into PC/Chol liposomes increases membrane rigidity which does not change after serum incubation. The presence of NPPE in liposomes decreases lipid transfer/exchange between liposomes and lipoproteins although the same amount of serum proteins were incorporated as in PC/Chol liposomes. As expected, these proteins are accessible to trypsin digestion. In accordance with these results, the liposome agglutination assay shows no steric barrier activity. As a whole, the results obtained in this paper suggest a complex mechanism for stabilization of NPPE containing liposomes in human serum.

Differential gene expression indicates that ‘buffalo hump’ is a distinct adipose tissue disturbance in HIV-1-associated lipodystrophy

Objective:To elucidate the molecular basis of the progressive enlargement of dorso-cervical adipose tissue, the so-called ‘buffalo hump’, that appears in a sub-set of patients with HIV-1/HAART-associated lipodystrophy. Design:Analysis of the expression of marker genes of mitochondrial function, adipogenesis, inflammation and cell proliferation in ten ‘buffalo hump’ samples and ten subcutaneous fat samples from HIV-1-infected/HAART-treated patients, and in ten healthy controls. Methods:Quantitative real-time polymerase chain reaction analysis of mitochondrial DNA and gene transcripts, and immunoblot for specific proteins. Results:‘Buffalo hump’ patients had lower levels of mitochondrial DNA and mitochondrial DNA-encoded transcripts with respect to healthy controls. The uncoupling protein (UCP)-1 gene was expressed only in ‘buffalo hump’ fat. There were no significant changes in the expression of UCP2, UCP3 or of marker genes of adipogenesis in ‘buffalo hump’ patients relative to healthy controls. ‘Buffalo hump’ fat did not show the high expression of tumor necrosis factor-α and β2-microglobulin identified in lipoatrophic subcutaneous fat from patients. The expression of the macrophage marker CD68 was also lower in ‘buffalo hump’ than in subcutaneous fat from patients. In contrast, ‘buffalo hump’ showed a higher expression of the cell proliferation marker PCNA. Conclusions:‘Buffalo hump’ adipose tissue shows specific disturbances in gene expression with respect to subcutaneous fat from HIV-1-infected/HAART-treated patients. Mitochondrial alterations cannot explain the differential behavior of ‘buffalo hump’ with respect to adipose depots prone to lipoatrophy. The absence of a local inflammatory status in ‘buffalo hump’ may explain in part the differential behavior of this adipose tissue.

9-cis-Retinoic Acid (9cRA), a Retinoid X Receptor (RXR) Ligand, Exerts Immunosuppressive Effects on Dendritic Cells by RXR-Dependent Activation: Inhibition of Peroxisome Proliferator-Activated Receptor γ Blocks Some of the 9cRA Activities, and Precludes Them to Mature Phenotype Development

At nanomolar range, 9-cis-retinoic acid (9cRA) was able to interfere in the normal differentiation process from human monocyte to immature dendritic cell (DC) and produced a switch in mature DCs to a less stimulatory mode than untreated cells. 9cRA-treated mature DCs secreted high levels of IL-10 with an IL-12 reduced production. The phenotypic alterations unleashed by 9cRA were similar but not identical to other specific retinoid X receptor (RXR) agonists and to those already reported for rosiglitazone, a PPARγ activator, on DCs. The simultaneous addition of 9cRA and rosiglitazone on DCs displayed additive effects. Moreover, addition to cultures of GW9662, a specific inhibitor of PPARγ, or the RXR pan-antagonist HX603, blocked these changes. All these results suggest an activation of PPARγ-RXR and other RXR containing dimers by 9cRA in DCs. Finally, both GW9662 and HX603 by themselves altered the maturation process unleashed by TNFα, poly(I:C) or LPS on human DCs further suggesting that the heterodimer PPARγ-RXR must fulfill a significant role in the physiological maturation process of these cells in addition to the repressing effects reported till now for this nuclear receptor.

Tumour necrosis factor alpha in fat redistribution syndromes associated with combination antiretroviral therapy in HIV-1-infected patients: potential role in subcutaneous adipocyte apoptosis.

Background  The pathogenesis of fat redistribution syndromes (FRS) observed in the setting of highly active antiretroviral therapy (HAART) for the treatment of HIV‐1‐infection remains elusive. A dysregulation of the tumour necrosis factor alpha (TNF‐α) system occurs in HIV‐infected patients with FRS.

Serum FGF21 levels are elevated in association with lipodystrophy, insulin resistance and biomarkers of liver injury in HIV-1-infected patients.

Objective:HIV-1-infected patients with lipodystrophy show insulin resistance, dyslipidemia and other signs of metabolic syndrome. Fibroblast growth factor-21 (FGF21) is a novel metabolic regulator that has been suggested to exert beneficial effects on metabolic homeostasis and insulin sensitivity. Our goal was to determine the relationship between FGF21 levels and metabolic alterations in these patients. Research design and methods:Serum FGF21 levels were analyzed in 179 individuals belonging to four groups: HIV-1-infected, antiretroviral-treated patients that have developed lipodystrophy (n = 59); HIV-1-infected, antiretroviral-treated patients without lipodystrophy (n = 45); untreated (naive) HIV-1-infected patients (n = 41); and healthy control individuals (n = 34). Serum FGF21 levels were correlated with parameters indicative of altered fat distribution, metabolic and cardiovascular risk, and in relation to HIV-1 infection and antiretroviral treatment regimens. Results:Serum FGF21 levels were increased in all HIV-1-infected patients, but the increases were most marked in those with lipodystrophy. FGF21 levels showed a strong positive correlation with indicators of lipodystrophy (trunk/apendicular fat ratio, waist-to-hip ratio), insulin resistance (fasting glucose, HOMA-R), dyslipidemia (low-density lipoprotein cholesterol), and liver injury (γ-glutamyltransferase). Conclusions:FGF21 levels are increased in HIV-1-infected patients, especially in those with lipodystrophy, and this increase is closely associated with insulin resistance, metabolic syndrome and makers of liver damage. Further research will be required to determine whether the increase in FGF21 levels is caused by a compensatory response or resistance to FGF21, and to establish the potential of FGF21 as a biomarker of altered metabolism in HIV-1-infected, antiretroviral-treated patients.