Ramanamurthy Boppana

CD40 Signaling Is Impaired in L. major–infected Macrophages and Is Rescued by a p38MAPK Activator Establishing a Host-protective Memory T Cell Response

Leishmania, a protozoan parasite, lives and multiplies as amastigote within macrophages. It is proposed that the macrophage expressed CD40 interacts with CD40 ligand on T cells to induce IFN-γ, a Th1-type cytokine that restricts the amastigote growth. Here, we demonstrate that CD40 cross-linking early after infection resulted in inducible nitric oxide synthetase type-2 (iNOS2) induction and iNOS2-dependent amastigote elimination. Although CD40 expression remained unaltered on L. major–infected macrophages, delay in the treatment of macrophages or of mice with anti-CD40 antibody resulted in significant reduction in iNOS2 expression and leishmanicidal function suggesting impaired CD40 signaling in Leishmania infection. The inhibition of CD40-induced iNOS2 expression by SB203580, a p38-mitogen activated protein kinase (p38MAPK)-specific inhibitor, and the reversal of the inhibition by anisomycin, a p38MAPK activator, suggested a crucial role of p38MAPK in CD40 signaling. Indeed, the CD40-induced p38MAPK phosphorylation, iNOS2 expression and anti-leishmanial function were impaired in Leishmania-infected macrophages but were restored by anisomycin. Anisomycins effects were reversed by SB203580 emphasizing the role of p38MAPK in CD40-induced iNOS2-dependent leishmanicidal function. Anisomycin administration in L. major–infected BALB/c mice resulted in significant reduction in the parasite load and established a host-protective Th1-type memory response. Also implicated in these findings is a scientific rationale to define novel anti-parasite drug targets and to bypass the problem of drug resistance.

Low plasma albumin levels are associated with increased plasma protein glycation and HbA1c in diabetes.

Albumin is one of the most abundant plasma proteins and is heavily glycated in diabetes. In this study, we have addressed whether variation in the albumin levels influence glycation of plasma proteins and HbA1c. The study was performed in three systems: (1) streptozotocin (STZ)-induced diabetic mice plasma, (2) diabetic clinical plasma, and (3) in vitro glycated plasma. Diabetic mice and clinical plasma samples were categorized as diabetic high albumin plasma (DHAP) and diabetic low albumin plasma (DLAP) on the basis of their albumin levels. For the in vitro experiment, two albumin levels, high albumin plasma (HAP) and low albumin plasma (LAP), were created by differential depletion of plasma albumin. Protein glycation was studied by using a combination of two-dimensional electrophoresis (2DE), Western blotting, and LC-MS(E). In both mice and clinical experiments, an increased plasma protein glycation was observed in DLAP than in DHAP. Additionally, plasma albumin levels were negatively correlated with HbA1c. The in vitro experiment with differential depletion of albumin mechanistically showed that the low albumin levels are associated with increased plasma protein glycation and that albumin competes for glycation with other plasma proteins.

HIV-1 Tat suppresses gp120-specific T cell response in IL-10-dependent manner.

A large number of multicomponent vaccine candidates are currently in clinical evaluation, many of which also include the HIV-1 Tat protein, an important regulatory protein of the virus. However, whether Tat, a known immune effector molecule with a well-conserved sequence among different HIV subtypes, affects the immune response to a coimmunogen is not well understood. In this study, using a bicistronic vector expressing both gp120 and Tat, we have analyzed the role of Tat in elicitation of the gp120-specific immune response. The T cell responses to gp120 were greatly diminished in mice coimmunized with Tat as compared with mice immunized with gp120 alone. This immunosuppressive activity of Tat was not confined to viral Ag only because it also suppressed the immune response of unrelated Ag. Analysis of the cytokine profile suggests that Tat induces IL-10 and since IL-10 has been demonstrated to have appreciable T cell inhibitory activity, it is plausible that IL-10 could be responsible for Tat-mediated immunosuppression. Finally, the immunosuppressive effect of Tat was not observed in IL-10-deficient mice, confirming the role of IL-10 in Tat-mediated immunosuppression. Thus, our results demonstrate for the first time that the immunosuppressive effect of Tat is mediated through IL-10 and suggests that Tat-induced IL-10-mediated immune suppression seems to cripple immune surveillance during HIV-1 infection.

Potential Dual Role of Eugenol in Inhibiting Advanced Glycation End Products in Diabetes: Proteomic and Mechanistic Insights

Medicinally important genus Ocimum harbors a vast pool of chemically diverse metabolites. Current study aims at identifying anti-diabetic candidate compounds from Ocimum species. Major metabolites in O. kilimandscharicum, O. tenuiflorum, O. gratissimum were purified, characterized and evaluated for anti-glycation activity. In vitro inhibition of advanced glycation end products (AGEs) by eugenol was found to be highest. Preliminary biophysical analysis and blind docking studies to understand eugenol-albumin interaction indicated eugenol to possess strong binding affinity for surface exposed lysines. However, binding of eugenol to bovine serum albumin (BSA) did not result in significant change in secondary structure of protein. In vivo diabetic mice model studies with eugenol showed reduction in blood glucose levels by 38% likely due to inhibition of α-glucosidase while insulin and glycated hemoglobin levels remain unchanged. Western blotting using anti-AGE antibody and mass spectrometry detected notably fewer AGE modified peptides upon eugenol treatment both in vivo and in vitro. Histopathological examination revealed comparatively lesser lesions in eugenol-treated mice. Thus, we propose eugenol has dual mode of action in combating diabetes; it lowers blood glucose by inhibiting α-glucosidase and prevents AGE formation by binding to ε-amine group on lysine, protecting it from glycation, offering potential use in diabetic management.

Proteome wide reduction in AGE modification in streptozotocin induced diabetic mice by hydralazine mediated transglycation

The non-enzymatic reaction between glucose and protein can be chemically reversed by transglycation. Here we report the transglycation activity of hydralazine using a newly developed MALDI-TOF-MS based assay. Hydralazine mediated transglycation of HbA1c, plasma proteins and kidney proteins was demonstrated in streptozotocin (STZ) induced diabetic mice, as evidenced by decrease in protein glycation, as well as presence of hydralazine-glucose conjugate in urine of diabetic mice treated with hydralazine. Hydralazine down regulated the expression of Receptor for Advanced Glycation End products (RAGE), NADPH oxidase (NOX), and super oxide dismutase (SOD). These findings will provide a new dimension for developing intervention strategies for the treatment of glycation associated diseases such as diabetes complications, atherosclerosis, and aging.

Albumin Competitively Inhibits Glycation of Less Abundant Proteins

Glycation, a non-enzymatic reaction between glucose and protein is the primary cause of diabetic complications. Albumin, the most abundant plasma protein undergoes glycation both in vivo and in vitro. The influence of albumin on glycation of less abundant proteins has not been addressed. For the first time, we show that albumin competitively inhibits the glycation of less abundant proteins. This study suggests that at least in the initial stages of diabetes, albumin may protect other proteins from glycation.

Discovery of rifampicin as a new anti-glycating compound by matrix-assisted laser desorption/ionization mass spectrometry-based insulin glycation assay

An in vitro insulin glycation assay was developed for screening glycation inhibitors. The assay involves the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for monitoring the formation of glycated insulin. The assay is simple, rapid and amenable for high throughput screening. Using this assay we have discovered a strong anti-glycation activity for the anti-tuberculosis drug rifampicin. These results were compared with bovine serum albumin glucose fluorescence assay. In addition, the IC50 of rifampicin was lower than that of aminoguanidine, a known anti-glycating agent, suggesting that rifampicin is a more potent glycation inhibitor.

Interleukin-12 is necessary for the priming of CD4+ T cells required during the elicitation of HIV-1 gp120-specific cytotoxic T-lymphocyte function.

The mechanism of the T‐cell response and cytokine induction to restrict human immunodeficiency virus 1 (HIV‐1) infection is not clear. During early infection, HIV‐infected individuals have a high frequency of virus‐specific cytotoxic T lymphocytes (CTLs) that effectively reduces the viral load. However, the CTLs are unable to clear the virus at later stages of infection, leading to disease progression. Dysregulation of cytokines like interleukin‐12 (IL‐12) and interferon‐γ (IFN‐γ) as a result of the interaction of HIV‐1‐specific T cells with antigen‐presenting cells is one of the possible causes of CTL dysfunction. Secretion of IL‐12 is reduced with the progression of HIV infection, correlating with impaired CTL function; however, the role of IL‐12 in CTL regulation awaits elucidation. Here, we have studied the role of IL‐12 in CTL dysfunction by using DNA immunization of wild‐type (WT) and IL‐12‐deficient mice with HIV‐1 gp120 complementary DNA. It was observed that the CTL response in IL‐12‐deficient mice was significantly less than that in WT mice. Our results further demonstrated that coimmunization with IL‐12 vector restored the impaired CTL response in IL‐12‐deficient mice. However, immunization with IL‐12 vector failed to rescue the CTL response in IFN‐γ deficient mice, suggesting that the CTL‐promoting function of IL‐12 is IFN‐γ‐mediated. Our data suggest a phase‐specific role of IL‐12 in the CTL response, specifically in the priming of CD4+ T cells that provide help to CD8+ T cells. Our results also suggest that IL‐12 is vital for the priming of antigen‐specific T cells and plays an essential role in IFN‐γ induction in T cells.

Proteomic insight reveals elevated levels of albumin in circulating immune complexes in diabetic plasma

A Hyperglycemic condition in diabetes promotes formation of advanced glycation end products, which are known to elicit immune response and form complexes with immunoglobulins called circulating immune complexes. To investigate the involvement of advanced glycation end product (AGE)-modified proteins in the elicitation of an immune response, circulating immune complexes were isolated and proteins associated were identified and characterized. Label-free-based mass spectrometric analysis of circulating immune complexes in clinical plasma of prediabetic, newly diagnosed diabetes, and diabetic microalbuminurea revealed elevated levels of serum albumin in the circulating immune complexes, which were also observed to be AGE modified. Further, to examine the role of glycation, circulating immune complexeswere analyzed in the streptozotocin-induced diabetic mice treated with or without aminoguanidine, a prototype glycation inhibitor. Mass spectrometric analysis of circulating immune complexes showed elevated levels of serum albumin in plasma from diabetic mice over that of control animals. Aminoguanidine-treated diabetic mice displayed decreased AGE modification of plasma albumin, accompanied by a reduced level of albumin in the circulating immune complexes. In addition, elevated levels of proinflammatory cytokines such as IL-1b, IL-2, and TNF-alpha were observed in diabetes, which were reduced with aminoguanidine treatment, suggesting the involvement of glycation in the immune response.

Molecules with O-acetyl group protect protein glycation by acetylating lysine residues

Pharmaceutical intervention for reduction of advanced glycation end products (AGEs) is considered as a therapeutic strategy to attenuate the pathogenesis of diabetes. Many molecules have been reported to possess antiglycation activity, one such example is acetylsalicylic acid (aspirin). It protects proteins from glycation by acetylating the lysine residues. Therefore, in this study we have synthesized and screened molecules containing free N-acetyl, O-acetyl and acetophenone groups. All the selected molecules in this study showed glycation inhibition but interestingly, only molecules with O-acetyl but not N-acetyl and acetophenone groups were capable of acetylating lysine residue. Furthermore, we have demonstrated that pre-acetylation or aspirin treatment prior to the induction of diabetes helps in reducing HbA1c and AGE formation in the streptozotocin induced diabetic mice. Hence pre-acetylation may have an additional therapeutic efficacy of reducing AGE levels in vivo. Incorporation of O-acetyl group into anti-diabetic molecules could be a useful strategy, as it may have an additive effect in reducing AGEs. Identification of such novel acetylating agents represents a new area in the drug discovery process.