Quels marqueurs osseux chez les patients hémodialysés : phosphatases alcalines osseuses ou ß-CrossLaps ?

BackgroundBone turnover (BT) abnormalities are frequently observed in patients with chronic kidney disease. Bone biopsy remains the gold standard for diagnosis; however, its invasive nature has led to its decreased utilisation. The serum parathyroid hormone (PTH) level is not a reliable bone marker (BM) for BT assessment. The latest international recommendations suggest the use of total alkaline phosphatase (t-ALP) or bone-specific alkaline phosphatase (b-ALP), but not ß-CrossLaps (CTX). We compared b-ALP, t-ALP, and CTX levels in patients on haemodialysis (HD).MethodsAll HD patients at a single institution following a standard 3 × 4 to 3 × 5 hours schedule were included in the study, provided they were free from liver disease. Serum intact PTH, t-ALP, b-ALP, and CTX values were compared at baseline and after 18 months of treatment. A kinetic study was performed for pre- and postdialysis CTX values over a 2-week period. We described the longitudinal evolution of these BMs in two typical patients.ResultsA total of 98 patients on HD (46% female) were evaluated. The mean age was 69.8 ± 11 years and the mean duration of dialysis was 54.4 ± 61 months. At baseline, CTX (2.1 ± 1 μg/L) correlated well with b-ALP (18 ± 11 μg/L; r = 0.64; P < 0.001) and PTH (221 ± 165 pg/mL; r = 0.62; P < 0.001). The changes in these values at 18 months were also correlated (ΔCTX compared with Δb-ALP: r = 0.51; P < 0.001; Δb-ALP compared with ΔPTH: r = 0.37, P < 0.01). b-ALP and t-ALP (245 ± 132 U/L) were closely correlated (r = 0.78), as was their variation over 18 months (r = 0.67), but t-ALP did not correlate with PTH, and correlated poorly with CTX (r = 0.38). The CTX reduction ratio during standard dialysis was approximately 70 to 75% over each session, although predialysis values remained stable.ConclusionIn HD patients, mean CTX values are five times higher than the normal range. CTX appears to be an alternative to b-ALP for assessing BT. b-ALP remains the standard BM, despite being expensive, infrequently available in many laboratories, and not useful for patients with liver disease.     

IL-13 induces expression of CD36 in human monocytes through PPARgamma activation

The class B scavenger receptor CD36 is a component of the pattern recognition receptors on monocytes that recognizes a variety of molecules. CD36 expression in monocytes depends on exposure to soluble mediators. We demonstrate here that CD36 expression is induced in human monocytes following exposure to IL-13, a Th2 cytokine, via the peroxisome proliferator-activated receptor (PPAR)gamma pathway. Induction of CD36 protein was paralleled by an increase in CD36 mRNA. The PPARgamma pathway was demonstrated using transfection of a PPARgamma expression plasmid into the murine macrophage cell line RAW264.7, expressing very low levels of PPARgamma, and in peritoneal macrophages from PPARgamma-conditional null mice. We also show that CD36 induction by IL-13 via PPARgamma is dependent on phospholipase A2 activation and that IL-13 induces the production of endogenous 15-deoxy-Delta12,14-prostaglandin J2, an endogenous PPARgamma ligand, and its nuclear localization in human monocytes. Finally, we demonstrate that CD36 and PPARgamma are involved in IL-13-mediated phagocytosis of Plasmodium falciparum-parasitized erythrocytes. These results reveal a novel role for PPARgamma in the alternative activation of monocytes by IL-13, suggesting that endogenous PPARgamma ligands, produced by phospholipase A2 activation, could contribute to the biochemical and cellular functions of CD36.     

Interleukin-12p40 overexpression promotes interleukin-12p70 and interleukin-23 formation but does not affect bacille Calmette-Guérin and Mycobacterium tuberculosis clearance

Interleukin (IL)-12p40, a subunit of IL-12p70 and IL-23, has previously been shown to inhibit IL-12p70 activity and interferon-gamma (IFN-gamma) production. However, recent evidence has suggested that the role of IL-12p40 is more complex. To study the contribution of IL-12p40 to immune responses against mycobacterial infections, we have used transgenic (tg) mice overexpressing IL-12p40 under the control of a major histocompatibility complex-II promoter. The IL-12p40 transgene was expressed during steady state at concentrations of 129 +/- 25 ng/ml of serum and 75 +/- 13 ng per spleen, while endogenous IL-12p40 was hardly detectable in control littermates. Bacille Calmette-Guérin (BCG) infection strongly induced the expression of IL-12p40 transgene in infected organs, and IL-12p40 monomeric and dimeric forms were identified in spleen of IL-12p40 tg mice. Excessive production of IL-12p40 resulted in a 14-fold increase in IL-12p70 serum levels in tg mice versus non-transgenic mice. IL-23 was also strongly elevated in the serum and spleens of IL-12p40 tg mice through BCG infection. While IFN-gamma and tumour necrosis factor protein levels were similar in IL-12p40 tg and non-transgenic mice, Th2 type immune responses were reduced in IL-12p40 tg mice. The number of BCG granulomas and macrophage expressing inducible nitric oxide synthase were similar in IL-12p40 tg and non-transgenic mice. IL-12p40 tg mice were as resistant as non-transgenic mice to BCG and Mycobacterium tuberculosis infections as they could efficiently control bacillary growth. These data show that high amounts of IL-12p40 promotes IL-12p70 and IL-23 formation, but that does not affect T helper 1 type immune responses and granuloma function, thus leading to normal mycobacterial clearance in infected organs.     

The Pseudomonas aeruginosa LasB metalloproteinase regulates the human urokinase-type plasminogen activator receptor through domain-specific endoproteolysis

Pseudomonas aeruginosa is an opportunistic pathogen in human lungs, where its secretable LasB metalloproteinase can be a virulence factor. The urokinase-type plasminogen activator receptor (uPAR) participates in pericellular proteolysis and the adherence/migration of epithelial cells and leukocytes recruited during infection and shows functional regulation by various proteinases via limited endoproteolysis occurring within its three domains (D1 to D3). We thus examined the proteolytic activity of LasB on uPAR by using recombinant uPAR as well as uPAR-expressing, human monocytic, and bronchial epithelial cell lines. Protein immunoblotting and flow immunocytometry using a panel of domain-specific anti-uPAR antibodies showed that LasB is able to cleave uPAR both within the sequence linking D1 to D2 and at the carboxy terminus of D3. Comparison of LasB-producing and LasB-deficient bacterial strains indicated that LasB is entirely responsible for the uPAR cleavage ability of P. aeruginosa. Based on amino-terminal protein microsequencing and mass spectrometry analysis of the cleavage of peptides mimicking the uPAR sequences targeted by LasB, cleavage sites were determined to be Ala(84)-Val(85) and Thr(86)-Tyr(87) (D1-D2) and Gln(279)-Tyr(280) (D3). Such a dual cleavage of uPAR led to the removal of amino-terminal D1, the generation of a truncated D2D3 species, and the shedding of D2D3 from cells. This proteolytic processing of uPAR was found to (i) drastically reduce the capacity of cells to bind urokinase and (ii) abrogate the interaction between uPAR and the matrix adhesive protein vitronectin. The LasB proteinase is thus endowed with a high potential for the alteration of uPAR expression and functioning on inflammatory cells during infections by P. aeruginosa.