Pathogenesis of scrapie in ARQ/ARQ sheep after subcutaneous infection: effect of lymphadenectomy and immune cell subset changes in relation to prion protein accumulation

It is well established that the infectious agent of scrapie can replicate in the lymphoreticular system (LRS). However, the effects of removal of LRS target tissues on the pathogenesis of the infection and the accumulation of disease-associated prion protein (PrP(d)) in LRS tissues on specific immune cell subsets are poorly understood aspects. To address these questions 16 ARQ/ARQ sheep were subcutaneously inoculated in the drainage area of the prefemoral lymph node with brain homogenate derived from Suffolk sheep naturally infected with scrapie. Fourteen sheep were then subjected to either early (14-17 days post-inoculation [dpi]) or late (175-201 dpi) lymphadenectomy and culled at preclinical or clinical stages of infection. Neither late nor even early lymphadenectomy prevented infection or had any effect on the accumulation of PrP(d) in the LRS or CNS suggesting a rapid organic dissemination of the infectious agent after inoculation. Lymph nodes from eight scrapie inoculated sheep selected on the basis of the amount of PrP(d) in their LRS tissues (negative, low or high) were examined for six different immune cell markers. The PrP(d) negative lymph nodes from two sheep with no evidence of scrapie infection showed lower numbers of cluster of determination (CD) 21 positive cells than PrP(d) positive nodes, irrespective of their location (hind leg or head). However, quantitative differences in the expression of this marker were not detected when comparing lymph nodes with low and high levels of PrP(d) accumulation, suggesting that proliferation of CD21 positive cells is related to scrapie infection, but not directly linked to the magnitude of PrP(d) accumulation. An additional observation of the study was that sheep that were methionin-threonine at codon 112 of the prion protein gene showed lower attack rates than methionine homozygotes (67% and 100%, respectively) and also generally lower levels of PrP(d) accumulation in the LRS and brain and increased survival times, suggesting an influence of such polymorphism in the susceptibility to scrapie.

Survival after the initiation of combination therapy in patients with pulmonary arterial hypertension: an Australian collaborative report

BACKGROUND

  Several cellular pathways are implicated in the pathogenesis of pulmonary arterial hypertension (PAH) and attempts to arrest disease progression with a single drug would not be expected to succeed in the medium term. In clinical practice, combination therapy is often used in patients deteriorating on monotherapy, despite the absence of firm evidence from randomized controlled controls.

METHODS

  From January 2005 to August 2009, 112 patients with World Health Organisation Functional Class (FC) II-IV PAH deteriorating on monotherapy received non-parenteral combination therapy at six Australian PAH expert hospitals. Combination therapy included bosentan, sitaxentan, ambrisentan, iloprost and sildenafil. Data were prospectively collected for survival status, 6-min walk distance, FC and echocardiographic parameters at the start of monotherapy through to commencement of combination therapy and at 6-monthly intervals thereafter.

RESULTS

  After varying periods of monotherapy (18.7±13.4onths), survival estimates on combination therapy were 88%, 71% and 61% for the additional 1, 2 and 3years respectively. Survival on dual therapy in patients with idiopathic PAH/familial PAH was 93% at 1year and 79% at 2years, and for scleroderma-related PAH, 72% at 1 year and 48% at year 2 after initiation of combination therapy. In survivors, dual therapy reversed the deterioration in FC, from 3.1±0.6 on monotherapy to 2.2±0.6 at 12months. Similarly, dual therapy improved 6-min walk distance from 316±119m to 406±129m at 12months, and sequential echocardiography demonstrated a fall in pulmonary artery systolic pressure and improved right ventricular function.

CONCLUSIONS

  Dual non-parenteral therapy appears safe and effective and should be considered for PAH patients who are deteriorating on monotherapy to improve long-term outcomes.

Hemodynamics in pulmonary arterial hypertension (PAH): do they explain long-term clinical outcomes with PAH-specific therapy?

Background

Pulmonary arterial hypertension (PAH) has witnessed dramatic treatment advances over the past decade. However, with the exception of epoprostenol, data from short-term randomized controlled trials (RCTs) have not shown a benefit of these drugs on survival. There remains a need to differentiate between available therapies and current endpoint responses which in turn, could be used to guide treatment selection and provide long-term prognostic information for patients.

Methods

We performed a systematic literature search of MEDLINE and EMBASE databases for RCTs of PAH-specific therapy published between January 1980 and May 2009. Articles were selected if they contained a placebo comparator and described hemodynamic changes from baseline. We applied the weighted mean change in hemodynamic variables to the equation developed by the National Institutes of Health (NIH) Registry to estimate long-term survival with each therapy.

Results

Ten RCTs involving 1,635 patients met the inclusion criteria. Suitable hemodynamic data were identified for bosentan, sitaxentan, sildenafil, epoprostenol, beraprost and treprostinil. 77.6% of patients were female and the mean (SD) age was 46.5 ± 4.9 years. 55.5% of patients had idiopathic PAH (iPAH), 23.9% PAH related to connective tissue disease, and 18.2% PAH related to congenital heart disease. Based on the effects observed in short-term trials and, relative to placebo, all analyzed therapies improved survival. The estimated 1-year survival was 78.4%, 77.8%, 76.1%, 75.8%, 75.2%, and 74.1% for epoprostenol, bosentan, treprostinil, sitaxentan, sildenafil, and beraprost, respectively. These estimates are considerably lower than the 1-year observed survival reported in several open-label and registry studies with PAH-specific therapies: 88% - 97%.

Conclusion

When applied to the NIH Registry equation, hemodynamic changes from baseline appear to underestimate the survival benefits observed with long-term PAH therapy.

Cellular nonmuscle myosins NMHC-IIA and NMHC-IIB and vertebrate heart looping

Flectin, a protein previously described to be expressed in a left-dominant manner in the embryonic chick heart during looping, is a member of the nonmuscle myosin II (NMHC-II) protein class. During looping, both NMHC-IIA and NMHC-IIB are expressed in the mouse heart on embryonic day 9.5. The patterns of localization of NMHC-IIB, rather than NMHC-IIA in the mouse looping heart and in neural crest cells, are equivalent to what we reported previously for flectin. Expression of full-length human NMHC-IIA and -IIB in 10 T1/2 cells demonstrated that flectin antibody recognizes both isoforms. Electron microscopy revealed that flectin antibody localizes in short cardiomyocyte cell processes extending from the basal layer of the cardiomyocytes into the cardiac jelly. Flectin antibody also recognizes stress fibrils in the cardiac jelly in the mouse and chick heart; while NMHC-IIB antibody does not. Abnormally looping hearts of the Nodal(Delta 600) homozygous mouse embryos show decreased NMHC-IIB expression on both the mRNA and protein levels. These results document the characterization of flectin and extend the importance of NMHC-II and the cytoskeletal actomyosin complex to the mammalian heart and cardiac looping.

Occurrence and cellular localization of PrPd in kidneys of scrapie-affected sheep in the absence of inflammation

Following a preliminary description of disease-associated prion protein (PrPd) deposition in the kidneys of scrapie-affected sheep, detailed studies have been undertaken in order to evaluate the factors that could account for such PrPd accumulation and to determine the precise location of PrPd in the renal papillae. Immunohistochemical (IHC) examinations for PrPd were conducted in kidneys collected at post-mortem from 30 naturally and 37 experimentally infected sheep. In addition, PrPd detection by western blot analysis (WB) and ultrastructural examination was carried out in a selection of kidneys. PrPd-specific, multifocal IHC labelling with antibody R145 was achieved in the kidneys of 44% and 51% of the naturally and experimentally infected sheep, respectively. The specificity of these results was confirmed by further IHC and WB using several PrP antibodies raised to different amino acid sequences, and by examination of control tissues. PrPd was shown to accumulate in the interstitium of the renal papillae, in association with the cell membrane and lysosomes of fibroblast-like cells, or extracellularly, in close contact with collagen and basal membranes. These deposits were unrelated to inflammatory changes in the kidney as shown by routine histology and by IHC for different immune cell markers. PrPd accumulated in the kidney of sheep that showed widespread PrPd deposition in the lymphoreticular system and had long incubation periods; these findings argue for a haematogenous origin of renal PrPd, although the precise site and mechanism-glomerular filtration and reabsorption at Henle's loop, or extravasation from vasa recta capillaries, or both-by which PrPd leaves the blood to accumulate in the interstitium of renal papillae remain to be determined. Either of these pathogenetic mechanisms could lead to environmental contamination via urine.