Elsa Kermorvant-Duchemin

The succinate receptor GPR91 in neurons has a major role in retinal angiogenesis

Vascularization is essential for tissue development and in restoration of tissue integrity after an ischemic injury. In studies of vascularization, the focus has largely been placed on vascular endothelial growth factor (VEGF), yet other factors may also orchestrate this process. Here we show that succinate accumulates in the hypoxic retina of rodents and, via its cognate receptor G protein–coupled receptor-91 (GPR91), is a potent mediator of vessel growth in the settings of both normal retinal development and proliferative ischemic retinopathy. The effects of GPR91 are mediated by retinal ganglion neurons (RGCs), which, in response to increased succinate levels, regulate the production of numerous angiogenic factors including VEGF. Accordingly, succinate did not have proangiogenic effects in RGC-deficient rats. Our observations show a pathway of metabolite signaling where succinate, acting through GPR91, governs retinal angiogenesis and show the propensity of RGCs to act as sensors of ischemic stress. These findings provide a new therapeutic target for modulating revascularization.

Retinopathy of prematurity: understanding ischemic retinal vasculopathies at an extreme of life

Retinopathy of prematurity (ROP) is a major complication of preterm birth. It encompasses a spectrum of pathologies that affect vision, from mild disease that resolves spontaneously to severe disease that causes retinal detachment and subsequent blindness. The pathologies are characterized by an arrest in normal retinal vascular development associated with microvascular degeneration. The resulting ischemia and retinal hypoxia lead to excessive abnormal compensatory blood vessel growth. However, this neovascularization can lead to fibrous scar formation and culminate in retinal detachment. Present therapeutic modalities to limit the adverse consequences of aberrant neovascularization are invasive and/or tissue-destructive. In this Review, we discuss current concepts on retinal microvascular degeneration, neovascularization, and available treatments, as well as present future perspectives toward more profound elucidation of the pathogenesis of ROP.

Trans-arachidonic acids generated during nitrative stress induce a thrombospondin-1-dependent microvascular degeneration.

Nitrative stress has an important role in microvascular degeneration leading to ischemia in conditions such as diabetic retinopathy and retinopathy of prematurity. Thus far, mediators of nitrative stress have been poorly characterized. We recently described that trans-arachidonic acids are major products of NO2•-mediated isomerization of arachidonic acid within the cell membrane, but their biological relevance is unknown. Here we show that trans-arachidonic acids are generated in a model of retinal microangiopathy in vivo in a NO•-dependent manner. They induce a selective time- and concentration-dependent apoptosis of microvascular endothelial cells in vitro, and result in retinal microvascular degeneration ex vivo and in vivo. These effects are mediated by an upregulation of the antiangiogenic factor thrombospondin-1, independently of classical arachidonic acid metabolism. Our findings provide new insight into the molecular mechanisms of nitrative stress in microvascular injury and suggest new therapeutic avenues in the management of disorders involving nitrative stress, such as ischemic retinopathies and encephalopathies.

Outcome and prognostic factors in neonates with septic shock.

Objective: Few accurate data are available on the outcome of septic shock in the neonatal period. The objective was to describe outcome and to determine variables associated with death or adverse outcome in neonates with septic shock. Design: Retrospective cohort study. Setting: A tertiary neonatal intensive care unit in a university hospital. Patients: All patients admitted to the neonatal intensive care unit over a 6-yr period meeting the following criteria: hypotension and/or need for intravenous fluid administration or vasoactive drugs, in the presence of proven or highly probable infection. Interventions: None. Measurements and Main Results: Main outcomes were 28-day mortality and adverse outcome at 18 months of corrected age, defined as death or severe sequelae (cerebral palsy, severe developmental delay, hearing impairment, blindness, or short bowel syndrome). Forty-eight infants were included. Follow-up data at 18 months were obtained for 46 of 48 infants. The 28-day mortality was 40% (19 deaths). Adverse outcome at 18 months of corrected age was observed in 24 of 46 infants (52%; death = 19, severe sequelae = 5). Twenty-eight percent of the infants were alive and had a normal examination at 18 months. Infants with adverse outcome had significantly lower gestational age, birth weight, Apgar score, weight at onset of sepsis, and pH and more often had Gram-negative infection, fetal growth restriction, hypoglycemia, and thrombocytopenia. Significant predictors (multivariate analysis) of 28-day mortality and of adverse outcome at 18 months of corrected age were weight (kg) at the onset of sepsis (odds ratio 0.14, 95% confidence interval 0.03–0.55; odds ratio 0.21, 95% confidence interval 0.06–0.74, respectively) and Gram-negative infection (odds ratio 10.1, 95% confidence interval 1.5–65.7; odds ratio 45.5, 95% confidence interval 3–637, respectively). Conclusions: Septic shock in the neonatal period has a very poor outcome. Data underscore the extreme vulnerability of very low birth weight infants to septic shock, particularly to Gram-negative species.

Parenteral Nutrition Objectives for Very Low Birth Weight Infants: Results of a National Survey

Objectives: The aim of the study was to evaluate parenteral nutrition objectives for very low birth weight (VLBW) infants in neonatal intensive care units (NICUs), and to compare nutritional protocol differences according to levels of care. Materials and Methods: A national survey was conducted in France through a questionnaire sent to 296 French neonatal departments to determine each team leaders nutritional objectives for parenteral nutrition of VLBW infants. Results: A total of 172 of the 296 French neonatal departments responded to the questionnaire. Protein administration was not started during the first day of life in half of the responding units. Furthermore, half of the units initiated protein administration with less than 1 g · kg−1 · day−1. The day of introduction of lipid emulsions varied considerably from one unit to another, but more than half of the units started the lipid emulsions after the third day of life. Twenty percent of the units reported a target energy intake of 100 kcal · kg−1 · day−1, whereas 14% reported a target intake above or equal to 130 kcal · kg−1 · day−1. Conclusions: In comparison with recent guidelines for parenteral nutrition for VLBW infants, the results indicate that the majority of the departments are familiar with target macronutrient and energy intakes, but the time of introduction and the rate of progression of macronutrients, particularly proteins and lipids, are frequently lower than those defined by the guidelines. The large-scale publication of new nutritional guidelines for the parenteral nutrition of neonates and preterm infants as well as regular, specific training in the parenteral nutrition of preterm infants are needed.

Understanding ischemic retinopathies: emerging concepts from oxygen-induced retinopathy

Ischemic retinopathies, such as retinopathy of prematurity and diabetic retinopathy are characterized by an initial microvascular degeneration, followed by an abnormal hypoxia-induced neovascularization. Oxygen-induced retinopathy (OIR) is a well-established in vivo model of ischemic retinopathies, which, although the triggering insult varies, all share a common end result of capillary loss. Understanding the mechanisms of normal retinal vascular development as well as the pathophysiological processes leading to the primary vascular loss is the key to develop treatments to prevent the sight-threatening neovascularization associated with human ischemic retinopathies. The importance of oxygen-dependant vascular endothelial growth factor in the pathophysiology of both phases of OIR has long been recognized. However, recent studies point out that OIR is a multifactorial disease, resulting from additive effects of an unbalanced expression of pro- and anti-angiogenic factors, interrelated with protective effects of nutritional factors and cytotoxic effects of oxidative and nitro-oxidative stress-dependant mediators. This review summarizes the most recent aspects of the research on OIR conducted in our laboratory and others, with a particular focus on the role of new mediators of nitro-oxidative stress, the trans-arachidonic acids, in microvascular degeneration, and on a novel pathway of metabolic signaling where hypoxia-driven succinate, via receptor GPR91, governs normal and pathological retinal angiogenesis.

Choroidal Involution Is a Key Component of Oxygen-Induced Retinopathy

PURPOSE Retinopathy of prematurity (ROP) is a major cause of visual handicap in the pediatric population. To date, this disorder is thought to stem from deficient retinal vascularization. Intriguingly, functional electrophysiological studies in patients with mild or moderate ROP and in the oxygen-induced retinopathy (OIR) model in rats reveal central photoreceptor disruption that overlies modest retinal vessel loss; a paucity of retinal vasculature occurs predominantly at the periphery. Given that choroidal circulation is the major source of oxygen and nutrients to the photoreceptors, the authors set out to investigate whether the choroidal vasculature system may be affected in OIR. METHODS Rat models of OIR treating newborn animals with 80% or 50/10% alternated oxygen level for the first two postnatal weeks were used to mimic ROP in humans. Immunohistology staining and vascular corrosion casts were used to investigate the vessel layout of the eye. To investigate the effect of 15-deoxy-Δ12,14-PGJ(2) (15d-PGJ(2); a nonenzymatic product of prostaglandin D(2)) on endothelial cells, in vitro cell culture and ex vivo choroid explants were employed and intravitreal injections were performed in animals. RESULTS The authors herein demonstrate that deficient vascularity occurs not only in the retinal plexus but also in the choroid. This sustained, marked choroidal degeneration is specifically confined to central regions of the retina that present persistent photoreceptor loss and corresponding functional deficits. Moreover, the authors show that 15d-PGJ(2) is a prominent contributor to this choroidal decay. CONCLUSIONS The authors demonstrate for the first time pronounced, sustained choroidal vascular involution during the development of ROP. Findings also suggest that effective therapeutic strategies to counter ROP should consider choroidal preservation.

Fatty acid receptor Gpr40 mediates neuromicrovascular degeneration induced by transarachidonic acids in rodents.

Objective—Nitro-oxidative stress exerts a significant role in the genesis of hypoxic-ischemic (HI) brain injury. We previously reported that the &ohgr;-6 long chain fatty acids, transarachidonic acids (TAAs), which are nitrative stress-induced nonenzymatically generated arachidonic acid derivatives, trigger selective microvascular endothelial cell death in neonatal neural tissue. The primary molecular target of TAAs remains unidentified. GPR40 is a G protein–coupled receptor activated by long chain fatty acids, including &ohgr;-6; it is highly expressed in brain, but its functions in this tissue are largely unknown. We hypothesized that TAAs play a significant role in neonatal HI-induced cerebral microvascular degeneration through GPR40 activation. Approach and Results—Within 24 hours of a HI insult to postnatal day 7 rat pups, a cerebral infarct and a 40% decrease in cerebrovascular density was observed. These effects were associated with an increase in nitrative stress markers (3-nitrotyrosine immunoreactivity and TAA levels) and were reduced by treatment with nitric oxide synthase inhibitor. GPR40 was expressed in rat pup brain microvasculature. In vitro, in GPR40-expressing human embryonic kidney (HEK)-293 cells, [14C]-14E-AA (radiolabeled TAA) bound specifically, and TAA induced calcium transients, extracellular signal–regulated kinase 1/2 phosphorylation, and proapoptotic thrombospondin-1 expression. In vivo, intracerebroventricular injection of TAAs triggered thrombospondin-1 expression and cerebral microvascular degeneration in wild-type mice, but not in GPR40-null congeners. Additionally, HI-induced neurovascular degeneration and cerebral infarct were decreased in GPR40-null mice. Conclusions—GPR40 emerges as the first identified G protein–coupled receptor conveying actions of nonenzymatically generated nitro-oxidative products, specifically TAAs, and is involved in (neonatal) HI encephalopathy.

Early chloride intake does not parallel that of sodium in extremely-low-birth-weight infants and may impair neonatal outcomes.

Background and Objective: Accurate data on the optimal chloride (Cl) intake in premature infants are scarce. The aim of the present study was to describe Cl intakes in the first 10 days of life and to assess the relations between high Cl intakes and corrected serum Cl level or markers of severe acidosis in infants <28 weeks’ gestation. Methods: Retrospective cohort study including all of the infants <28 weeks admitted to the neonatal intensive care unit during a 3-year period and cared for from birth until day 10 or more. Results: Fifty-six infants were included. Cumulative total Cl intakes reached 9.6 ± 3.7 mmol/kg at day 3 and 49.2 ± 13.5 mmol/kg at day 10. Inadvertent intakes (from intravenous fluids other than parenteral nutrition) represented on average 70% of total Cl intakes in the first 3 days. Difference between Cl and sodium intakes reached 7.8 ± 4.8 mmol/kg at day 10 and mainly originated from parenteral nutrition. By multivariate analysis, cumulative Cl intake >10 mmol/kg during the first 3 days was an independent risk factor of base excess <−10 mmol/L. Cumulative Cl intake >45 mmol/kg during the first 10 days was an independent risk factor of corrected chloremia >115 mmol/L and of base excess <−10 mmol/L. Conclusions: Cumulative Cl intake >10 mmol/kg during the first 3 days (ie, 3.3 mmol · kg−1 · day−1 on average) and >45 mmol/kg during the first 10 days (ie, 4.5 mmol · kg−1 · day−1 on average) may have unwanted metabolic consequences and should be avoided. Imbalance between electrolytes provided by the parenteral nutrition solution need to be detected and corrected.

Neonatal Hyperglycemia Inhibits Angiogenesis and Induces Inflammation and Neuronal Degeneration in the Retina

Recent evidence suggests that transient hyperglycemia in extremely low birth weight infants is strongly associated with the occurrence of retinopathy of prematurity (ROP). We propose a new model of Neonatal Hyperglycemia-induced Retinopathy (NHIR) that mimics many aspects of retinopathy of prematurity. Hyperglycemia was induced in newborn rat pups by injection of streptozocine (STZ) at post natal day one (P1). At various time points, animals were assessed for vascular abnormalities, neuronal cell death and accumulation and activation of microglial cells. We here report that streptozotocin induced a rapid and sustained increase of glycemia from P2/3 to P6 without affecting rat pups gain weight or necessitating insulin treatment. Retinal vascular area was significantly reduced in P6 hyperglycemic animals compared to control animals. Hyperglycemia was associated with (i) CCL2 chemokine induction at P6, (ii) a significant recruitment of inflammatory macrophages and an increase in total number of Iba+ macrophages/microglia cells in the inner nuclear layer (INL), and (iii) excessive apoptosis in the INL. NHIR thereby reproduces several aspects of ischemic retinopathies, including ROP and diabetic retinopathies, and might be a useful model to decipher hyperglycemia-induced cellular and molecular mechanisms in the small rodent.