Multiple stiffening effects of nanoscale knobs on human red blood cells infected with Plasmodium falciparum malaria parasite

During its asexual development within the red blood cell (RBC), Plasmodium falciparum (Pf), the most virulent human malaria parasite, exports proteins that modify the host RBC membrane. The attendant increase in cell stiffness and cytoadherence leads to sequestration of infected RBCs in microvasculature, which enables the parasite to evade the spleen, and leads to organ dysfunction in severe cases of malaria. Despite progress in understanding malaria pathogenesis, the molecular mechanisms responsible for the dramatic loss of deformability of Pf-infected RBCs have remained elusive. By recourse to a coarse-grained (CG) model that captures the molecular structures of Pf-infected RBC membrane, here we show that nanoscale surface protrusions, known as “knobs,” introduce multiple stiffening mechanisms through composite strengthening, strain hardening, and knob density-dependent vertical coupling. On one hand, the knobs act as structural strengtheners for the spectrin network; on the other, the presence of knobs results in strain inhomogeneity in the spectrin network with elevated shear strain in the knob-free regions, which, given its strain-hardening property, effectively stiffens the network. From the trophozoite to the schizont stage that ensues within 24–48 h of parasite invasion into the RBC, the rise in the knob density results in the increased number of vertical constraints between the spectrin network and the lipid bilayer, which further stiffens the membrane. The shear moduli of Pf-infected RBCs predicted by the CG model at different stages of parasite maturation are in agreement with experimental results. In addition to providing a fundamental understanding of the stiffening mechanisms of Pf-infected RBCs, our simulation results suggest potential targets for antimalarial therapies.The most virulent human malaria parasite, Plasmodium falciparum (Pf), causes ∼700,000 deaths each year (1, 2). Following entry into red blood cells (RBCs), the parasite matures through the ring (0–24 h), trophozoite (24–36 h), and schizont stages (40–48 h). This intraerythrocyte maturation is accompanied by striking changes in the surface topography and membrane architecture of the infected RBC (3–5). A notable modification is the formation of nanoscale protrusions, commonly known as knobs, at the RBC surface during the second half (24–48 h) of the asexual cycle. These protrusions mainly comprise the knob-associated histidine-rich protein (KAHRP) and the membrane-embedded cytoadherence protein, Pf-erythrocyte membrane protein 1 (PfEMP1). KAHRP binds to the fourth repeat unit of the spectrin α-chain, to ankyrin, to spectrin–actin–protein 4.1 complexes, and to the cytoplasmic domain of PfEMP1 (6–9). These attachments enhance the vertical coupling between the lipid bilayer and the spectrin network. Another striking modification in the Pf-infected RBC membrane is the reorganization of the cytoskeletal network caused by parasite-induced actin remodeling (10). As a result of these molecular-level modifications, the Pf-infected RBC exhibits markedly increased stiffness [the shear modulus increases on average from ∼4−10 µN/m in normal/uninfected RBCs, to ∼40 µN/m at the trophozoite stage, and to as high as 90 µN/m at the schizont stage (11–13)] and cytoadherence to the vascular endothelium, which enable sequestration from circulation in vasculature, and evasion from the surveillance mechanisms of the spleen. Although in vitro experimental studies have revealed roles of particular parasite-encoded proteins in remodeling the host RBC (14–22), the mechanism by which Pf-infected RBCs gain dramatically increased stiffness has remained unclear. Indeed, uncertainty remains as to whether the loss of deformability arises from the structural reorganization of the host membrane components or from the deposition of parasite proteins. That is, it is not clear whether the stiffening is due to remodeling of the spectrin network, or to the formation of the knobs, or both. As experimental studies alone have heretofore not been able to determine the molecular details, numerical modeling, combined with a variety of experimental observations and measurements, offers an alternative approach to reveal the underlying mechanisms.We present here a coarse-grained (CG) molecular dynamics (MD) RBC membrane model to correlate structural modifications at the molecular ultrastructure level with the shear responses of the Pf-infected RBC membrane, focusing on the second half of the parasite’s intra-RBC asexual cycle (24–48 h), i.e., the trophozoite and schizont stages. The CG model is computationally efficient, and able to capture the molecular structures of the RBC membrane in both normal and infected states. CGMD simulations reveal that spectrin network remodeling accounts for a relatively small change in shear modulus. Instead, the knobs stiffen the membrane by multiple mechanisms, including composite strengthening, strain hardening, and knob density-dependent vertical coupling. Our findings provide molecular-level understanding of the stiffening mechanisms operating in Pf-infected RBCs and shed light on the pathogenesis of falciparum malaria.     

Bremsstrahlung parameters of praseodymium-142 in different human tissues: a dosimetric perspective for 142Pr radionuclide therapy

Objective

Praseodymium-142 [T _1/2?=?19.12?h, $ E_{\beta^{-}}$ ?=?2.162?MeV (96.3%), E???=?1575?keV (3.7%)] is one of the ¹⁴¹Pr radioisotopes. Many studies have been attempted to assess the significance of usage ¹⁴²Pr in radionuclide therapy. In many studies, the dosimetric parameters of ¹⁴²Pr sources were calculated by modeling ¹⁴²Pr sources in the water phantom and scoring the energy deposited around it. However, the medical dosimetry calculations in water phantom consider Bremsstrahlung production, raising the question: ??How important is to simulate human tissues instead of using water phantom??? This study answers these questions by estimation of ¹⁴²Pr Bremsstrahlung parameters.

Methods

The Bremsstrahlung parameters of ¹⁴²Pr as therapeutic beta nuclides in different human tissues (adipose, blood, brain, breast, cell nucleus, eye lens, gastrointestinal tract, heart, kidney, liver, lung deflated, lymph, muscle, ovary, pancreas, cartilage, red marrow, spongiosa, yellow marrow, skin, spleen, testis, thyroid and different skeleton bones) were calculated by extending the national council for radiation protection model. The specific Bremsstrahlung constant (?? _Br), probability of energy loss by beta during Bremsstrahlung emission (P _Br) and Bremsstrahlung activity (A _release)_Br were estimated. It should be mentioned that Monte Carlo simulation was used for estimation of ¹⁴²Pr Bremsstrahlung activity based on the element compositions of different human tissues and the calculated exposures from the anthropomorphic phantoms.

Results

?? _Br for yellow marrow was smallest amount (1.1962?×?10^?3 C/kg-cm²/MBq-h) compared to the other tissues and highest for cortical bone (2.4764?×?10^?3 C/kg-cm²/MBq-h), and, overall, ?? _Br for skeletal tissues were greater than other tissues. In addition, ?? _Br breast was 1.8261?×?10^?3 C/kg-cm²/MBq-h which was greater than sacrum and spongiosa bones. Moreover, according to (A _release)_Br of ¹⁴²Pr, the patients receiving ¹⁴²Pr do not have to be hospitalized for radiation precautions and the Bremsstrahlung production does not prevent the therapy for outpatients.

Conclusion

However, modeling ¹⁴²Pr source in water phantom for simulation of ¹⁴²Pr source in soft tissues could be acceptable due to similarity of ?? _Br in water and soft tissues; this approximation is a gross computation in the mediums encompassing high atomic numbers. These data may be practical in the investigation of Bremsstrahlung absorbed dose where ¹⁴²Pr is involved in radionuclide therapy.     

Reliability of a patient survey assessing ＂Short Form Injury Questionnaire 7＂ in Iran

Objective: Injury is a major cause of morbidity and mortality in the world.The assessment of patterns and severity of injury in high-risk groups is crucial for planning and service development.On a lar...     

Office Evaluation of Male Patients with Lower Urinary Tract Symptoms

Lower urinary tract symptoms due to benign prostatic hyperplasia (LUTS/BPH) are one of the most common urologic disorders in men. Accurate history-taking and focused physical examination allows us to diagnose the majority of cases. A better understanding of risk factors helps us tailor our treatment and predict outcomes more accurately. Population studies are crucial in our understanding of LUTS/BPH natural history. Temporary prostatic urethral stents that are used for the management of urinary retention may also be used for evaluation of patients with detrusor hypo-contractility. The use of ultrasound to measure intravesical prostatic protrusion (IPP) and the Doppler study for prostate capsular artery resistive index are promising. Near-infrared spectroscopy (NIRS) examines the tissue oxygenation that may be affected by bladder outlet obstruction. The mathematical algorithm needs some fine-tuning, and its reproducibility is debatable. Serum and urinary biomarkers may help us to diagnose the disorder, and more effectively monitor patients?? response to therapy. Among all, IPP is clinically more applicable at this time.     

Intestinal fungal and parasitic infections in kidney transplant recipients: a multi-center study

Kidney transplant recipients are susceptible to various infections due to the use of immunosuppressive drugs. The present study was performed as studies on the prevalence of intestinal fungal and parasitic infections in kidney transplant recipients are limited. A total of 150 kidney transplant recipients and 225 matched immunocompetent outpatients, who were referred to the laboratory of Noor Hospital, Isfahan, were studied. After recording demographic characteristics, direct test and specific laboratory cultures were carried out on the stool specimens. Patients were instructed on sanitary rules and, during each medical visit, they were reminded of the same. The overall prevalence of intestinal parasitic and fungal infections was 33.3% and 58.7%, respectively, in transplant recipients and 20% and 51%, respectively, in the control group; the difference was not statistically significant. The most prevalent intestinal parasite was Entameba coli, which was seen in 9.3% of the study patients and 6.7% of the controls. The most prevalent fungus was Candida sp., which was seen in 22% of the study patients and 24.4% of the control group. Co-existing infection with two or more fungi was seen in 14.8% and 3.4% in the case and control groups, respectively; P <0.001. Interestingly, there was no significant difference in the prevalence of infection by a single organism between the two groups. However, co-existing infection with two or more species was more prevalent in transplant recipients. We conclude that further investigations are needed to evaluate the pathogenesis of infection with these microorganisms.     

Bacterial Analysis of Peri-implantitis and Chronic Periodontitis in Iranian Subjects

Chronic periodontitis (CP) and peri-implantitis (PI) are multifactorial diseases of tooth and implant supporting apparatus. Bacterial invasion and consequent host immune response seem to play a role in relevant pathogenesis. The structural differences between tooth and implant pose preferential biofilm colonization. This study was aimed to compare the prevalence of bacteria in CP and PI. Clinical and radiographic examination performed over 69 individuals referred to Shahid Beheshti Dental School (Tehran, Iran) and four groups categorized: CP (n=22), HP (n=21), PI (n=13) and HI (n=13). The mean age was 45.6 years, 55% of participants were female and 45% were male. Bacterial samples were collected by paper point method and transferred to Institute of Odontology, University of Gothenburg (Gothenburg, Sweden) for checkerboard DNA-DNA hybridization. Kruskal-Wallis and Mann-Whitney U tests were used to compare distribution of bacteria in four groups. Significant differences were observed for T. forsythia, P. intermedia, C. rectus, P. endodontic, P. gingivalis, T. denticola and P. tannerae (P<0.05). The most prevalent bacteria in CP and PI were T. forsythia and P. gingivalis, respectively. In conclusion, bacterial prevalence differs significantly between tooth and implant. The most prevalent bacteria in Iranian subpopulation do not necessarily bear a resemblance to other populations. The type of implant surface may influence the biofilm. Other studies should be conducted to corroborate these findings.