Endothelial Glycocalyx Impairment in Disease: Focus on Hyaluronan Shedding.

Hyaluronan (HA) is a ubiquitous glycosaminoglycan of the extracellular matrix. It is present in the endothelial glycocalyx covering the apical surface of endothelial cells. The endothelial glycocalyx regulates blood vessel permeability and homeostasis. HA plays a central role in numerous functions of the endothelial surface layer, protecting the endothelial cells, regulating the barrier permeability, and ensuring mechanosensing, which is essential to nitric oxide production and flow-induced vasodilation. During acute injury, inflammatory conditions, or many other pathologic conditions, the endothelial glycocalyx is damaged, and its degradation is accompanied by shedding of one or more glycocalyx components into the blood. Syndecan-1, heparan sulfate, and HA are the main components whose shedding has been claimed to represent the endothelial glycocalyx state of health. This review focuses on endothelial glycocalyx HA and highlights its key roles in the functions of the endothelial glycocalyx, its shedding in several pathologic conditions such as sepsis, diabetes, chronic and acute kidney injury, ischemia/reperfusion, atherosclerosis, and inflammation, which are all accompanied by increased circulating HA levels. Plasma/serum HA level is becoming recognized as a biomarker of endothelial glycocalyx damage in select pathologies. Hyaluronidase, the main HA-degrading enzyme, and its involvement in the impairment of endothelial glycocalyx are also addressed.

Platelet hyaluronidase-2 regulates the early stages of inflammatory disease in colitis.

Platelets are specialized cells essential for hemostasis that also function as crucial effectors capable of mediating inflammatory and immune responses. These sentinels continually survey their environment and discriminate between homeostatic and danger signals such as modified components of the extracellular matrix. The glycosaminoglycan hyaluronan (HA) is a major extracellular matrix component that coats the vascular lumen and, under normal conditions, restricts access of inflammatory cells. In response to tissue damage, the endothelial HA matrix enhances leukocyte recruitment and regulates the early stages of the inflammatory response. We have shown that platelets can degrade HA from the surface of activated endothelial cells via the enzyme hyaluronidase-2 (HYAL2) and that HYAL2 is deficient in platelets isolated from patients with inflammatory bowel disease (IBD). Platelets are known to be involved in the pathogenesis of several chronic disease states, including IBD, but they have been largely overlooked in the context of intestinal inflammation. We therefore wanted to define the mechanism by which platelet HYAL2 regulates the inflammatory response during colitis. In this study, we provide evidence that HA catabolism is disrupted in human intestinal microvascular endothelial cells isolated from patients with IBD. Furthermore, mice deficient in HYAL2 are more susceptible to an acute model of colitis, and this increased susceptibility is abrogated by transfusion of HYAL2-competent platelets. Finally, we show that platelets, via HYAL2-dependent degradation of endothelial HA, regulate the early stages of inflammation in colitis by limiting leukocyte extravasation.

Endothelial Glycocalyx as a Shield Against Diabetic Vascular Complications: Involvement of Hyaluronan and Hyaluronidases.

The endothelial glycocalyx (EG), which covers the apical surface of the endothelial cells and floats into the lumen of the vessels, is a key player in vascular integrity and cardiovascular homeostasis. The EG is composed of PGs (proteoglycans), glycoproteins, glycolipids, and glycosaminoglycans, in particular hyaluronan (HA). HA seems to be implicated in most of the functions described for EG such as creating a space between blood and the endothelium, controlling vessel permeability, restricting leukocyte and platelet adhesion, and allowing an appropriate endothelial response to flow variation through mechanosensing. The amount of HA in the EG may be regulated by HYAL (hyaluronidase) 1, the most active somatic hyaluronidase. HYAL1 seems enriched in endothelial cells through endocytosis from the bloodstream. The role of the other main somatic hyaluronidase, HYAL2, in the EG is uncertain. Damage to the EG, accompanied by shedding of one or more of its components, is an early sign of various pathologies including diabetes mellitus. Shedding increases the blood or plasma concentration of several EG components, such as HA, heparan sulfate, and syndecan. The plasma levels of these molecules can then be used as sensitive markers of EG degradation. This has been shown in type 1 and type 2 diabetic patients. Recent experimental studies suggest that preserving the size and amount of EG HA in the face of diabetic insults could be a useful novel therapeutic strategy to slow diabetic complications. One way to achieve this goal, as suggested by a murine model of HYAL1 deficiency, may be to inhibit the function of HYAL1. The same approach may succeed in other pathological situations involving endothelial dysfunction and EG damage.

Hyaluronan Does Not Regulate Human Epidermal Keratinocyte Proliferation and Differentiation.

Hyaluronan (HA) is synthesized by three HA synthases (HAS1, HAS2, and HAS3) and secreted in the extracellular matrix. In human skin, large amounts of HA are found in the dermis. HA is also synthesized by keratinocytes in the epidermis, although its epidermal functions are not clearly identified yet. To investigate HA functions, we studied the effects of HA depletion on human keratinocyte physiology within in vitro reconstructed human epidermis. Inhibition of HA synthesis with 4-methylumbelliferone (4MU) did not modify the expression profile of the epidermal differentiation markers involucrin, keratin 10, and filaggrin during tissue reconstruction. In contrast, when keratinocytes were incubated with 4MU, cell proliferation was decreased. In an attempt to rescue the proliferation function, HA samples of various mean molecular masses were added to keratinocyte cultures treated with 4MU. These samples were unable to rescue the initial proliferation rate. Furthermore, treatments with HA-specific hyaluronidase, although removing almost all HA from keratinocyte cultures, did not alter the differentiation or proliferation processes. The differences between 4MU and hyaluronidase effects did not result from differences in intracellular HA, sulfated glycosaminoglycan concentration, apoptosis, or levels of HA receptors, all of which remained unchanged. Similarly, knockdown of UDP-glucose 6-dehydrogenase (UGDH) using lentiviral shRNA effectively decreased HA production but did not affect proliferation rate. Overall, these data suggest that HA levels in the human epidermis are not directly correlated with keratinocyte proliferation and differentiation and that incubation of cells with 4MU cannot equate with HA removal.

Hyaluronan Depolymerization by Megakaryocyte Hyaluronidase-2 Is Required for Thrombopoiesis.

Hyaluronan is the predominant glycosaminoglycan component of the extracellular matrix with an emerging role in hematopoiesis. Modulation of hyaluronan polymer size is responsible for its control over cellular functions, and the balance of hyaluronan synthesis and degradation determines its molecular size. Although two active somatic hyaluronidases are expressed in mammals, only deficiency in hyaluronidase-2 (Hyal-2) results in thrombocytopenia of unknown mechanism. Our results reveal that Hyal-2 knockout mice accumulate hyaluronan within their bone marrow and within megakaryocytes, the cells responsible for platelet generation. Proplatelet formation by Hyal-2 knockout megakaryocytes was disrupted because of abnormal formation of the demarcation membrane system, which was dilated and poorly developed. Importantly, peptide-mediated delivery of exogenous hyaluronidase rescued deficient proplatelet formation in murine and human megakaryocytes lacking Hyal-2. Together, our data uncover a previously unsuspected mechanism of how hyaluronan and Hyal-2 control platelet generation.

Respective roles of hyaluronidases 1 and 2 in endogenous hyaluronan turnover.

We studied the physiologic roles of the hyaluronidase (HYAL) 1 and HYAL2 in hyaluronan (HA) turnover. HA was localized and quantified using HA binding proteins in various tissues of Hyal1(-/-) and Hyal2(-/-) mice (knockout mice) as well as control mice. HA MW was determined using gel filtration chromatography. HA endocytosis in liver nonparenchymal cells (NPCs) was quantified in vivo Both Hyal1 and Hyal2 knockout mice showed HA accumulation in peripheral tissues without changes in HA MW distribution. HYAL2 deficiency induced buildup of very high MW (>3.10(6) Da) HA in lymph and serum with severe lymph node distortion. The lack of HYAL2 also impaired high MW HA endocytosis by liver NPCs. HYAL1 deficiency led to a moderate increase in serum HA concentration without changes in HA MW distribution and to HA overload of liver NPCs. Wild-type C57BL/6 mice served as controls. In HA injection experiments, saline-injected mice served as additional controls. We conclude that: 1) HYAL1 and HYAL2 are both needed for tissue HA catabolism; 2) HYAL2 is required for high MW HA clearance in lymph nodes and plasma and for HA endocytosis by liver NPCs; and 3) the main role of HYAL1 is HA degradation within liver NPCs.-Bourguignon, V., Flamion, B. Respective roles of hyaluronidases 1 and 2 in endogenous hyaluronan turnover.

Subcellular trafficking and activity of Hyal-1 and its processed forms in murine macrophages.

The hyaluronidase Hyal-1 is an acid hydrolase that degrades hyaluronic acid (HA), a component of the extracellular matrix. It is often designated as a lysosomal protein. Yet few data are available on its intracellular localization and trafficking. We demonstrate here that in RAW264.7 murine macrophages, Hyal-1 is synthesized as a glycosylated precursor that is only weakly mannose 6-phosphorylated. Nevertheless, this precursor traffics to endosomes, via a mannose 6-phosphate-independent secretion/recapture mechanism that involves the mannose receptor. Once in endosomes, it is processed into a lower molecular mass form that is transported to lysosomes, where its activity could be detected using native gel zymography. Indeed, this activity co-distributed with lysosomal hydrolases in the densest fraction of a self-forming Percoll(TM) density gradient. Moreover, it shifted toward the lower density region, in parallel with those hydrolases, when a decrease of lysosomal density was induced by the endocytosis of sucrose. Interestingly, the activity of the processed form of Hyal-1 was largely underestimated when assayed by zymography after SDS-PAGE and subsequent renaturation of the proteins, by contrast to the full-length protein that could efficiently degrade HA in those conditions. These results suggest that noncovalent associations support the lysosomal activity of Hyal-1.

Recommendations for the conduct of clinical trials for drugs to treat or prevent sarcopenia.

PURPOSE: Sarcopenia is an age-related muscle condition which is frequently a precursor of frailty, mobility disability and premature death. It has a high prevalence in older populations and presents a considerable social and economic burden. Potential treatments are under development but, as yet, no guidelines support regulatory studies for new drugs to manage sarcopenia. The objective of this position paper is therefore to suggest a set of potential endpoints and target population definitions to stimulate debate and progress within the medico-scientific and regulatory communities. METHODS: A multidisciplinary expert working group was hosted by the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis, which reviewed and discussed the recent literature from a perspective of clinical experience and guideline development. Relevant parallels were drawn from the development of definition of osteoporosis as a disease and clinical assessment of pharmaceutical treatments for that indication. RESULTS: A case-finding decision tree is briefly reviewed with a discussion of recent prevalence estimations of different relevant threshold values. The selection criteria for patients in regulatory studies are discussed according to the aims of the investigation (sarcopenia prevention or treatment) and the stage of project development. The possible endpoints of such studies are reviewed and a plea is made for the establishment of a core outcome set to be used in all clinical trials of sarcopenia. CONCLUSIONS: The current lack of guidelines for the assessment of new therapeutic treatments for sarcopenia could potentially hinder the delivery of effective medicines to patients at risk.

Lack of hyaluronidases exacerbates renal post-ischemic injury, inflammation, and fibrosis.

Renal ischemia-reperfusion injury (IRI) is a pathological process that may lead to acute renal failure and chronic dysfunction in renal allografts. During IRI, hyaluronan (HA) accumulates in the kidney, but suppression of HA accumulation during IRI protects the kidney from ischemic insults. Here we tested whether Hyal1-/- and Hyal2-/- mice display exacerbated renal damage following unilateral IRI due to a higher HA accumulation in the post-ischemic kidney compared with that in the kidney of wild-type mice. Two days after IRI in male mice there was accumulation of HA and CD44 in the kidney, marked tubular damage, infiltration, and increase creatininemia in wild-type mice. Knockout mice exhibited higher amounts of HA and higher creatininemia. Seven days after injury, wild-type mice had a significant decrease in renal damage, but knockout mice still displayed exacerbated inflammation. HA and CD44 together with α-smooth muscle actin and collagen types I and III expression were increased in knockout compared with wild-type mice 30 days after IRI. Thus, both HA-degrading enzymes seem to be protective against IRI most likely by reducing HA accumulation in the post-ischemic kidney and decreasing the inflammatory processes. Deficiency in either HYAL1 or HYAL2 leads to enhanced HA accumulation in the post-ischemic kidney and consequently worsened inflammatory response, increased tubular damage, and fibrosis.

Deficiency in mouse hyaluronidase 2: a new mechanism of chronic thrombotic microangiopathy.

Hyaluronan is a major component of the extracellular matrix and glycocalyx. Its main somatic degrading enzymes are hyaluronidases 1 and 2, neither of which is active in the bloodstream. We generated hyaluronidase 2-deficient mice. These animals suffer from chronic, mild anemia and thrombocytopenia, in parallel with a 10-fold increase in plasma hyaluronan concentration. In this study we explored the mechanism of these hematologic anomalies. The decreased erythrocyte and platelet counts were attributed to peripheral consumption. The erythrocyte half-life was reduced from 25 to 8 days without signs of premature aging. Hyaluronidase 2-deficient platelets were functional. Major intrinsic defects in erythrocyte membrane or stability, as well as detrimental effects of high hyaluronan levels on erythrocytes, were ruled out in vitro. Normal erythrocytes transfused into hyaluronidase 2-deficient mice were quickly destroyed but neither splenectomy nor anti-C5 administration prevented chronic hemolysis. Schistocytes were present in blood smears from hyaluronidase 2-deficient mice at a level of 1% to 6%, while virtually absent in control mice. Hyaluronidase 2-deficient mice had increased markers of endothelial damage and microvascular fibrin deposition, without renal failure, accumulation of ultra-large multimers of von Willebrand factor, deficiency of A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motifs, member 13 (ADAMTS13), or hypertension. There was no sign of structural damage in hepatic or splenic sinusoids, or in any other microvessels. We conclude that hyaluronidase 2 deficiency induces chronic thrombotic microangiopathy with hemolytic anemia in mice. The link between this uncommon condition and hyaluronidase 2 remains to be explored in humans.

Murine hyaluronidase 2 deficiency results in extracellular hyaluronan accumulation and severe cardiopulmonary dysfunction.

Hyaluronidase (HYAL) 2 is a membrane-anchored protein that is proposed to hydrolyze hyaluronan (HA) to smaller fragments that are internalized for breakdown. Initial studies of a Hyal2 knock-out (KO) mouse revealed a mild phenotype with high serum HA, supporting a role for HYAL2 in HA breakdown. We now describe a severe cardiac phenotype, deemed acute, in 54% of Hyal2 KO mice on an outbred background; Hyal2 KO mice without the severe cardiac phenotype were designated non-acute. Histological studies of the heart revealed that the valves of all Hyal2 KO mice were expanded and the extracellular matrix was disorganized. HA was detected throughout the expanded valves, and electron microscopy confirmed that the accumulating material, presumed to be HA, was extracellular. Both acute and non-acute Hyal2 KO mice also exhibited increased HA in the interstitial extracellular matrix of atrial cardiomyocytes compared with control mice. Consistent with the changes in heart structure, upper ventricular cardiomyocytes in acute Hyal2 KO mice demonstrated significant hypertrophy compared with non-acute KO and control mice. When the lungs were examined, evidence of severe fibrosis was detected in acute Hyal2 KO mice but not in non-acute Hyal2 KO or control mice. Total serum and heart HA levels, as well as size, were increased in acute and non-acute Hyal2 KO mice compared with control mice. These findings indicate that HYAL2 is essential for the breakdown of extracellular HA. In its absence, extracellular HA accumulates and, in some cases, can lead to cardiopulmonary dysfunction. Alterations in HYAL2 function should be considered as a potential contributor to cardiac pathologies in humans.

Mouse liver lysosomes contain enzymatically active processed forms of Hyal-1.

It has long been known that liver lysosomes contain an endoglycosidase activity able to degrade the high molecular mass glycosaminoglycan hyaluronic acid (HA). The identification and cloning of a hyaluronidase with an acidic pH optimum, Hyal-1, suggested it might be responsible for this activity. However, we previously reported that this hydrolase could only be detected in pre-lysosomal compartments of the mouse liver using a zymography technique that allows the detection of Hyal-1 activity after SDS-PAGE ("renatured protein zymography"). Present work reveals that the activity highlighted by this technique belongs to a precursor form of Hyal-1 and that the lysosomal HA endoglycosidase activity of the mouse liver is accounted for by a proteolytically processed form of Hyal-1 that can only be detected using "native protein zymography". Indeed, the distribution of this form follows the distribution of ß-galactosidase, a well-established lysosomal marker, after fractionation of the mouse liver in a linear sucrose density gradient. In addition, both activities shift toward the lower density region of the gradient when a specific decrease of the lysosomal density is induced by Triton WR-1339 injection. The fact that only native protein zymography but not renatured protein zymography is able to detect Hyal-1 activity in lysosomes points to a non-covalent association of Hyal-1 proteolytic fragments or the existence of closely linked partners supporting Hyal-1 enzymatic activity. The knockdown of Hyal-1 results in an 80% decrease of total acid hyaluronidase activity in the mouse liver, confirming that Hyal-1 is a key actor of HA catabolism in this organ.

Patients' Preferences for Systemic Lupus Erythematosus Treatments-A Discrete Choice Experiment.

BACKGROUND: Symptoms of systemic lupus erythematosus (SLE) vary between patients, but those of increased disease activity typically include musculoskeletal and mucocutaneous manifestations such as joint pain, swelling, and rashes. Several treatment options are available to patients with SLE with variable efficacy. Many treatments, especially corticosteroids, cause unwanted side effects, although little is currently known about patients' preferences for treatments of SLE. OBJECTIVE: We aimed to identify which attributes of SLE treatment are valued by patients and to quantify their relative importance. METHODS: Adult participants with moderate-to-severe SLE were asked to make a series of choices between two hypothetical treatments in an online discrete choice experiment (DCE). A latent class model (LCL) was estimated to analyze choice data. Relative attribute importance (RAI) was calculated to determine the importance of each attribute to participants. RESULTS: A total of 342 participants from the USA completed the survey. A three-class LCL model was found to have the best fit. Class 1 (non-attenders) had non-significant preferences across all attributes. To achieve a better fit, a constrained LCL (cLCL) model was run with the two remaining classes. The most important attributes for participants in class 2 (benefit-seekers) were joint pain (RAI = 32.0%), non-joint pain (RAI = 21.8%), fatigue (RAI = 20.1%), and skin rashes and itching (RAI = 19.1%). The most important attributes for participants in class 3 (risk-avoiders) were risk of non-severe side effects from corticosteroids (RAI = 28.4%), risk of severe side effects from corticosteroids (RAI = 21.4%), and the risk of infections (RAI = 19.2%). Risk-avoiders were more likely to have been diagnosed with SLE for a longer period (>1 year) and were more likely to have experience with oral corticosteroids. CONCLUSIONS: SLE patients fall into two groups with distinct preferences: benefit-seekers, who prioritize reducing the impact of disease symptoms, and risk-avoiders, who prioritize avoiding treatment risks. The implication of this finding will depend on the reasons for these differences, which warrant further research. Our study suggests that these differences arise due to the impact of disease and treatment experience on preferences. If so, well-informed patients may not be willing to tolerate the risks associated with oral corticosteroids in exchange for their benefits.

Meaningful Within-Patient Change in Subjective Total Sleep Time in Patients with Insomnia Disorder: An Analysis of the Sleep Diary Questionnaire Using Data from Open-Label and Phase III Clinical Trials.

BACKGROUND: The Sleep Diary Questionnaire (SDQ), a modified version of the Consensus Sleep Diary, is a 17-item sleep diary for assessing subjective total sleep time (sTST: total time spent asleep at night) and other sleep parameters in insomnia trials. sTST is a key parameter of efficacy in insomnia trials; however, the magnitude of improvement in this parameter that people with insomnia disorder consider clinically meaningful is unclear. OBJECTIVE: The aim of this study was to estimate meaningful within-patient change for sTST using clinical trial data. METHODS: Data were from an open-label trial of zolpidem and pooled data from a phase III placebo-controlled trial of daridorexant. In both trials, adults with moderate to severe insomnia completed the SDQ daily. Meaningful change in sTST was estimated in an anchor-based analysis using outcome measures that were correlated with change in weekly average sTST (Spearman correlation coefficient ≥ 0.30): the Insomnia Severity Index, patient global assessments and impressions of severity and change in daytime and night-time symptoms (PGA-S, PGI-S, PGI-C), and clinician global impressions of severity and change in patients' daytime symptoms (CGI-S, CGI-C). Meaningful within-patient change estimates were 'triangulated' to identify a value where they converged. RESULTS: In the open-label trial (N = 114), subjects with a 1-point or 1-step improvement on the anchors had mean increases in sTST of 60.1-83.2 min at day 8 and 55.5-68.2 min at day 15. For subjects with a 2-point or 2-step improvement on the anchors, mean increases in sTST were 79.6-81.4 min at day 8 and 80.1-93.5 min at day 15. In the phase III trial (N = 930), weekly average increases in sTST for subjects with a 1-point or 1-step improvement on the anchors were 39.3-46.7 min at month 1 and 47.3-58.3 min at month 3. For subjects with a 2-point or 2-step improvement on the anchors, mean increases in sTST were 60.7-76.2 min at month 1 and 70.1-87.7 min at month 3. Triangulation of these values supported a meaningful within-patient change threshold starting at 55 min. CONCLUSION: Increasing sTST is an important treatment outcome for people with insomnia. An increase in sleep time of approximately 55 min is meaningful to patients. CLINICAL TRIALS REGISTRATION: NCT03056053 (17 February 2017) and NCT03545191 (4 June 2018).

Cascading renal injury after brain death: Unveiling glycocalyx alteration and the potential protective role of tacrolimus.

Brain death (BD) is a complex medical state that triggers systemic disturbances and a cascade of pathophysiological processes. This condition significantly impairs both kidney function and structural integrity, thereby presenting considerable challenges to graft viability and the long-term success of transplantation endeavors. Tacrolimus (FK506), an immunosuppressive drug, was used in this study to assess its impact as a pretreatment on brain death-induced renal injury. This study aimed to investigate changes associated with brain death-induced renal injury in a 4-month-old female porcine model. The experimental groups included brain death placebo-pretreated (BD; n = 9), brain death tacrolimus-pretreated using the clinical dose of 0.25 mg/kg the day before surgery, followed by 0.05 mg/kg/day 1 hour before the procedure (BD + FK506; n = 8), and control (ctrl, n = 7) piglets, which did not undergo brain death induction. Furthermore, we aimed to assess the effect of FK506 on these renal alterations through graft preconditioning. We hypothesized that immunosuppressive properties of FK506 reduce tissue inflammation and preserve the glycocalyx. Our findings revealed a series of interconnected events triggered by BD, leading to a deterioration of renal function and increased proteinuria, increased apoptosis in the vessels, glomeruli and tubules, significant leukocyte infiltration into renal tissue, and degradation of the glycocalyx in comparison with ctrl group. Importantly, treatment with FK506 demonstrated significant efficacy in attenuating these adverse effects. FK506 helped reduce apoptosis, maintain glycocalyx integrity, regulate neutrophil infiltration, and mitigate renal injury following BD. This study offers new insights into the pathophysiology of BD-induced renal injury, emphasizing the potential of FK506 pretreatment as a promising therapeutic intervention for organ preservation, through maintaining endothelial function with the additional benefit of limiting the risk of rejection.

Health technology assessment in osteoporosis.

We review the various aspects of health technology assessment in osteoporosis, including epidemiology and burden of disease, and assessment of the cost-effectiveness of recent advances in the treatment of osteoporosis and the prevention of fracture, in the context of the allocation of health-care resources by decision makers in osteoporosis. This article was prepared on the basis of a symposium held by the Belgian Bone Club and the discussions surrounding that meeting and is based on a review and critical appraisal of the literature. Epidemiological studies confirm the immense burden of osteoporotic fractures for patients and society, with lifetime risks of any fracture of the hip, spine, and forearm of around 40 % for women and 13 % for men. The economic impact is also large; for example, Europe's six largest countries spent €31 billion on osteoporotic fractures in 2010. Moreover, the burden is expected to increase in the future with demographic changes and increasing life expectancy. Recent advances in the management of osteoporosis include novel treatments, better fracture-risk assessment notably via fracture risk algorithms, and improved adherence to medication. Economic evaluation can inform decision makers in health care on the cost-effectiveness of the various interventions. Cost-effectiveness analyses suggest that the recent advances in the prevention and treatment of osteoporosis may constitute an efficient basis for the allocation of scarce health-care resources. In summary, health technology assessment is increasingly used in the field of osteoporosis and could be very useful to help decision makers efficiently allocate health-care resources.

Inhibition of hyaluronan is protective against renal ischaemia-reperfusion injury.

BACKGROUND: Ischaemia-reperfusion injury (IRI) to the kidney is a complex pathophysiological process that leads to acute renal failure and chronic dysfunction in renal allografts. It was previously demonstrated that during IRI, hyaluronan (HA) accumulates in the cortical and external medullary interstitium along with an increased expression of its main receptor, CD44, on inflammatory and tubular cells. The HA-CD44 pair may be involved in persistent post-ischaemic inflammation. Thus, we sought to determine the role of HA in the pathophysiology of ischaemia-reperfusion (IR) by preventing its accumulation in post-ischaemic kidney. METHODS: C57BL/6 mice received a diet containing 4-methylumbelliferone (4-MU), a potent HA synthesis inhibitor. At the end of the treatment, unilateral renal IR was induced and mice were euthanized 48 h or 30 days post-IR. RESULTS: 4-MU treatment for 14 weeks reduced the plasma HA level and intra-renal HA content at 48 h post-IR, as well as CD44 expression, creatininemia and histopathological lesions. Moreover, inflammation was significantly attenuated and proliferation was reduced in animals treated with 4-MU. In addition, 4-MU-treated mice had a significantly reduced expression of α-SMA and collagen types I and III, i.e. less renal fibrosis, 30 days after IR compared with untreated mice. CONCLUSION: Our results demonstrate that HA plays a significant role in the pathogenesis of IRI, perhaps in part through reduced expression of CD44. The suppression of HA accumulation during IR may protect renal function against ischaemic insults.

HIGH-MOLECULAR-WEIGHT HYALURONAN-A POTENTIAL ADJUVANT TO FLUID RESUSCITATION IN ABDOMINAL SEPSIS?

ABSTRACT: While fluid resuscitation is fundamental in the treatment of sepsis-induced tissue hypoperfusion, a sustained positive fluid balance is associated with excess mortality. Hyaluronan, an endogenous glycosaminoglycan with high affinity to water, has not been tested previously as adjuvant to fluid resuscitation in sepsis. In a prospective, parallel-grouped, blinded model of porcine peritonitis sepsis, we randomized animals to intervention with adjuvant hyaluronan (add-on to standard therapy, n = 8) or 0.9% saline (n = 8). After the onset of hemodynamic instability, the animals received an initial bolus of 0.1% hyaluronan (1 mg/kg/10 min) or placebo (0.9% saline) followed by a continuous infusion of 0.1% hyaluronan (1 mg/kg/h) or saline during the experiment. We hypothesized that the administration of hyaluronan would reduce the volume of fluid administered (aiming at stroke volume variation <13%) and/or attenuate the inflammatory reaction. Total volumes of intravenous fluids infused were 17.5 ± 11 versus 19.0 ± 7 mL/kg/h in intervention and control groups, respectively ( P = 0.442). Plasma IL-6 increased to 2,450 (1,420-6,890) pg/mL and 3,690 (1,410-11,960) pg/mL (18 hours of resuscitation) in the intervention and control groups (nonsignificant). The intervention counteracted the increase in proportion of fragmented hyaluronan associated with peritonitis sepsis (mean peak elution fraction [18 hours of resuscitation] intervention group: 16.8 ± 0.9 versus control group: 17.9 ± 0.6 [ P = 0.031]). In conclusion, hyaluronan did not reduce the volume needed for fluid resuscitation or decrease the inflammatory reaction, even though it counterbalanced the peritonitis-induced shift toward increased proportion of fragmented hyaluronan.

Synthesis and fragmentation of hyaluronan in renal ischaemia.

BACKGROUND: The turnover of hyaluronan (HA), especially the production of low-molecular-weight fragments of HA, was examined in a model of unilateral renal ischaemia-reperfusion (IR) in rats. METHODS: HA was extracted from the outer and inner stripe of the outer medulla (OSOM and ISOM) at different times following IR. Its fragmentation was measured using membrane filtration and size-exclusion chromatography. Quantitative reverse transcription-polymerase chain reaction, zymography and immunohistochemistry were used to assess the expression and localization of various forms of HA synthase (HAS) and hyaluronidase (HYAL). Macrophage infiltration was evaluated using immunohistochemistry. RESULTS: HA accumulated at Day 1 mostly as high-molecular-weight (HMW) species with an elution profile similar to a reference 2500 kDa HA and at Day 14 mostly as medium- to low-size fragments. Within 1 day, HAS1 messenger RNA was up-regulated > 50- and 35-fold in OSOM and ISOM, respectively. Thereafter, HAS1 tended to normalize, while HAS2 increased steadily. Both synthetic enzymes were localized around tubules and in the interstitium. Conversely, HYAL1, HYAL2 and global hyaluronidase activity were repressed during the first 24 h. The patterns were identical in the OSOM and ISOM despite markedly different amounts of HA at baseline. There was no obvious correlation between HA deposits and macrophage infiltration. CONCLUSIONS: In the post-ischaemic kidney, HA starts to accumulate at Day 1 mostly as HMW species. Later on, a large proportion becomes degraded into smaller fragments. This pattern is explained by coordinated changes in the expression of HA synthases and hyaluronidases, especially an early induction of HAS1. The current data open the door to timed pharmacological interventions blocking the production of HA fragments.

Pre-market clinical evaluations of innovative high-risk medical devices in Europe.

OBJECTIVES: High-quality clinical evidence is most often lacking when novel high-risk devices enter the European market. At the same time, a randomized controlled trial (RCT) is often initiated as a requirement for obtaining market access in the US. Should coverage in Europe be postponed until RCT data are available? We studied the premarket clinical evaluation of innovative high-risk medical devices in Europe compared with the US, and with medicines, where appropriate. METHODS: The literature and regulatory documents were checked. Representatives from industry, Competent Authorities, Notified Bodies, Ethics Committees, and HTA agencies were consulted. We also discuss patient safety and the transparency of information. RESULTS: In contrast to the US, there is no requirement in Europe to demonstrate the clinical efficacy of high-risk devices in the premarket phase. Patients in Europe can thus have earlier access to a potentially lifesaving device, but at the risk of insufficiently documented efficacy and safety. Variations in the stringency of clinical reviews, both at the level of Notified Bodies and Competent Authorities, do not guarantee patient safety. We tried to document the design of premarket trials in Europe and number of patients exposed, but failed as this information is not made public. Furthermore, the Helsinki Declaration is not followed with respect to the registration and publication of premarket trials. CONCLUSIONS: For innovative high-risk devices, new EU legislation should require the premarket demonstration of clinical efficacy and safety, using an RCT if possible, and a transparent clinical review, preferably centralized.