Treatment planning and dosimetric comparison study on two different volumetric modulated arc therapy delivery techniques

Aim

To compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.

Background

Volumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.

Materials and methods

Ten patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50 Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.

Results

RapidArc plans achieved the best conformity (CI_95% = 1.08 ± 0.07) while Elekta VMAT plans were slightly inferior (CI_95% = 1.10 ± 0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12 ± 0.02 Gy when compared to RapidArc with 0.08 ± 0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92 ± 2.90) Gy when compared to RapidArc (7.83 ± 3.31) Gy. The integral dose is found to be inferior with Elekta VMAT (11.50 ± 6.49) × 10⁴ Gy cm³ when compared to RapidArc (13.11 ± 7.52) × 10⁴ Gy cm³. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3 mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.

Conclusion

The study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation.     

Removal of acidic residues of the prodomain of PCSK9 increases its activity towards the LDL receptor

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low density lipoprotein receptor (LDLR) at the cell surface and mediates intracellular degradation of the LDLR. The amino-terminus of mature PCSK9, residues 31–53 of the prodomain, has an inhibitory effect on this function of PCSK9, but the underlying mechanism is not fully understood. In this study, we have identified two highly conserved negatively charged segments (residues 32–40 and 48–50, respectively) within this part of the prodomain and performed deletions and substitutions to study their importance for degradation of the LDLRs.Deletion of the acidic residues of the longest negatively charged segment increased PCSK9’s ability to degrade the LDLR by 31%, whereas a modest 8% increase was observed when these residues were mutated to uncharged amino acids. Thus, both the length and the charge of this part of the prodomain were important for its inhibitory effect. Deletion of the residues of the shorter second negatively charged segment only increased PCSK9’s activity by 8%. Substitution of the amino acids of both charged segments to uncharged residues increased PCSK9’s activity by 36%. These findings indicate that the inhibitory effect of residues 31–53 of the prodomain is due to the negative charge of this segment. The underlying mechanism could involve the binding of this peptide segment to positively charged structures which are important for PCSK9’s activity. One possible candidate could be the histidine-rich C-terminal domain of PCSK9.     

Serum levels of interleukin-13 and interferon-gamma from adult patients with asthma in Mysore

Serum protein analysis for noninvasive quantification of airway inflammation in asthma is a promising research tool in the field of lung diseases. Cytokines are believed to have major role in inflammatory process of the airways of the lung. There is an imbalance between T-helper (Th)-2 cells, which secrete interleukin (IL)-4 and interleukin (IL)-13, and Th1 cells, which secrete interferon (IFN)-gamma in asthma. To test the hypothesis that serum IL-13 and IL-4 levels may be elevated whereas IFN-gamma would be decreased in this cohort of patients, a property that could make them possible candidate biomarkers in determining asthma occurrence and severity, we measured concentrations of IL-4, IL-13 and IFN-gamma in serum samples of 88 subjects (44 normal, 12 with mild asthma, 16 with moderate asthma, and 16 with severe asthma). Serum Levels of IL-4, IL-13, and IFN-gamma were determined by an enzyme-linked immune-sorbent assay (ELISA). Median serum level of IFN-gamma in asthmatic patients was 8.0pg/ml, while it was 11.4pg/ml in healthy controls. However, the difference was not significant. Among the different age groups in whom IFN-gamma was assessed, the highest median value in both cases and controls was observed in the age group of 31-40years. The median serum level of IL-13 was 40.0pg/ml in asthmatic patients and 58.25pg/ml in healthy controls. The difference was not significant. On subgroup analysis, no significant difference of IFN-gamma and IL-13 between asthma of different severities was observed. The study also revealed nonsignificant difference of serum cytokines with the duration of asthma, number of allergens, and severity of sensitization. Normal serum levels of IFN-gamma and IL-13 in asthmatic patients suggest their neutral role in the inflammatory process; however, more studies are required to establish the effect of these cytokines in adulthood asthma in different ethnic populations.     

Investigations on the evolutionary conservation of PCSK9 reveal a functionally important protrusion

Proprotein convertase subtilisin/kexin type 9 (PCSK9) interferes with the recycling of low-density lipoprotein (LDL) receptor (LDLR). This leads to LDLR degradation and reduced cellular uptake of plasma LDL. Naturally occurring human PCSK9 loss-of-function mutations are associated with low levels of plasma LDL cholesterol and a reduced risk of coronary heart disease. PCSK9 gain-of-function mutations result in lower LDL clearance and increased risk of atherosclerosis. The exact mechanism by which PCSK9 disrupts the normal recycling of LDLR remains to be determined. In this study, we have assembled homologs of human PCSK9 from 20 vertebrates, a cephalochordate and mollusks in order to search for conserved regions of PCSK9 that may be important for the PCSK9-mediated degradation of LDLR. We found a large, conserved protrusion on the surface of the PCSK9 catalytic domain and have performed site-directed mutagenesis experiments for 13 residues on this protrusion. A cluster of residues that is important for the degradation of LDLR by PCSK9 was identified. Another cluster of residues, at the opposite end of the conserved protrusion, appears to be involved in the physical interaction with a putative inhibitor of PCSK9. This study identifies the residues, sequence segments and surface patches of PCSK9 that are under strong purifying selection and provides important information for future studies of PCSK9 mutants and for investigations on the function of this regulator of cholesterol homeostasis.     

Sonic hedgehog-Dependent Induction of MicroRNA 31 and MicroRNA 150 Regulates Mycobacterium bovis BCG-Driven Toll-Like Receptor 2 Signaling

Hedgehog (HH) signaling is a significant regulator of cell fate decisions during embryogenesis, development, and perpetuation of various disease conditions. Testing whether pathogen-specific HH signaling promotes unique innate recognition of intracellular bacteria, we demonstrate that among diverse Gram-positive or Gram-negative microbes, Mycobacterium bovis BCG, a vaccine strain, elicits a robust activation of Sonic HH (SHH) signaling in macrophages. Interestingly, sustained tumor necrosis factor alpha (TNF-α) secretion by macrophages was essential for robust SHH activation, as TNF-α^−/− macrophages exhibited compromised ability to activate SHH signaling. Neutralization of TNF-α or blockade of TNF-α receptor signaling significantly reduced the infection-induced SHH signaling activation both in vitro and in vivo. Intriguingly, activated SHH signaling downregulated M. bovis BCG-mediated Toll-like receptor 2 (TLR2) signaling events to regulate a battery of genes associated with divergent functions of M1/M2 macrophages. Genome-wide expression profiling as well as conventional gain-of-function or loss-of-function analysis showed that SHH signaling-responsive microRNA 31 (miR-31) and miR-150 target MyD88, an adaptor protein of TLR2 signaling, thus leading to suppression of TLR2 responses. SHH signaling signatures could be detected in vivo in tuberculosis patients and M. bovis BCG-challenged mice. Collectively, these investigations identify SHH signaling to be what we believe is one of the significant regulators of host-pathogen interactions.     

Synthesis of antitrypanosomal 1,2-dioxane derivatives based on a natural product scaffold

A short practical synthesis of a new natural product based scaffold (6), based on antitrypanosomal and antimalarial compounds isolated from different Plakortis species is described. The scaffold contains a peroxide unit that is surprisingly stable to chemical manipulation elsewhere in the molecule, enabling it to be elaborated into a small library of derivatives. It is stable to ozonolysis, reductive work-up with dimethylsulfide and the Wittig reaction with stabilized phosphorus ylides. The scaffold along with its Wittig analogues has displayed low to sub-micro molar (0.2-3.3 μM) antitrypanosomal activity.     

Ac2PIM-responsive miR-150 and miR-143 Target Receptor-interacting Protein Kinase 2 and Transforming Growth Factor Beta-activated Kinase 1 to Suppress NOD2-induced Immunomodulators

Specific and coordinated regulation of innate immune receptor-driven signaling networks often determines the net outcome of the immune responses. Here, we investigated the cross-regulation of toll-like receptor (TLR)2 and nucleotide-binding oligomerization domain (NOD)2 pathways mediated by Ac₂PIM, a tetra-acylated form of mycobacterial cell wall component and muramyl dipeptide (MDP), a peptidoglycan derivative respectively. While Ac₂PIM treatment of macrophages compromised their ability to induce NOD2-dependent immunomodulators like cyclooxygenase (COX)-2, suppressor of cytokine signaling (SOCS)-3, and matrix metalloproteinase (MMP)-9, no change in the NOD2-responsive NO, TNF-α, VEGF-A, and IL-12 levels was observed. Further, genome-wide microRNA expression profiling identified Ac₂PIM-responsive miR-150 and miR-143 to target NOD2 signaling adaptors, RIP2 and TAK1, respectively. Interestingly, Ac₂PIM was found to activate the SRC-FAK-PYK2-CREB cascade via TLR2 to recruit CBP/P300 at the promoters of miR-150 and miR-143 and epigenetically induce their expression. Loss-of-function studies utilizing specific miRNA inhibitors establish that Ac₂PIM, via the miRNAs, abrogate NOD2-induced PI3K-PKCδ-MAPK pathway to suppress β-catenin-mediated expression of COX-2, SOCS-3, and MMP-9. Our investigation has thus underscored the negative regulatory role of Ac₂PIM-TLR2 signaling on NOD2 pathway which could broaden our understanding on vaccine potential or adjuvant utilities of Ac₂PIM and/or MDP.