Exquisite exposure: Formaldehyde as a metabolic regulator.

Throughout life, whether through external consumption or internal production, we are exposed to different reactive metabolites considered toxic to the body. Pham et al.1 uncover metabolic regulation by one such harmful metabolite: formaldehyde.

Levosulpiride for the treatment of diabetic macular oedema: a phase 2 randomized clinical trial.

BACKGROUND/OBJECTIVE: The prokinetic levosulpiride elevates vasoinhibin levels in the vitreous of patients with proliferative diabetic retinopathy (PDR) suggesting clinical benefits due to the anti-vasopermeability and anti-angiogenic properties of vasoinhibin. We investigated the biological activity of levosulpiride in centre-involving diabetic macular oedema (DME). PATIENTS/METHODS: Prospective, randomized, double-blinded, dual-centre, phase 2 trial in patients with centre-involving DME orally treated with placebo (n = 17) or levosulpiride (n = 17) for 8 weeks or in patients with PDR undergoing elective pars plana vitrectomy and receiving placebo (n = 18) or levosulpiride (n = 18) orally for the 1 week before vitrectomy. RESULTS: Levosulpiride improved changes from baseline in best-corrected visual acuity (p ≤ 0.037), central foveal thickness (CFT, p ≤ 0.013), and mean macular volume (MMV, p ≤ 0.002) at weeks 4, 6, and 8 compared to placebo. At 8 weeks, the proportion of eyes gaining ≥5 ETDRS letters at 4 m (41% vs. 28%), losing ≥21 µm in CFT (55% vs. 28%), and dropping ≥0.06 mm3 in MMV (65% vs. 29%) was higher after levosulpiride than placebo. The overall grading of visual and structural parameters improved with levosulpiride (p = 0.029). Levosulpiride reduced VEGF (p = 0.025) and PlGF (p = 0.008) levels in the vitreous of PDR patients. No significant adverse side-effects were detected. CONCLUSIONS: Oral levosulpiride for 8 weeks improved visual and structural outcomes in patients with centre-involving DME by mechanisms that may include intraocular upregulation of vasoinhibin and downregulation of VEGF and PlGF. Larger clinical trials evaluating long-term efficacy and safety are warranted.

Sulpiride-induced hyperprolactinaemia increases retinal vasoinhibin and protects against diabetic retinopathy in rats.

Excessive vasopermeability and angiogenesis compromise vision in diabetic macular oedema (DME) and diabetic retinopathy (DR). Vasoinhibin is a fragment of the hormone prolactin (PRL) that inhibits diabetes-induced retinal hypervasopermeability and ischaemia-induced retinal angiogenesis in rodents. Hyperprolactinaemia generated by the dopamine D2 receptor antagonist, levosulpiride, is associated with higher levels of vasoinhibin in the vitreous of patients with DR, implying a beneficial outcome due to vasoinhibin-mediated inhibition of retinal vascular alterations. Here, we tested whether hyperprolactinaemia induced by racemic sulpiride increases intraocular vasoinhibin levels and inhibits retinal hypervasopermeability in diabetic rats. Diabetes was generated with streptozotocin and, 4 weeks later, rats were treated for 2 weeks with sulpiride or osmotic minipumps delivering PRL. ELISA, Western blot, and Evans blue assay were used to evaluate serum PRL, retinal vasoinhibin, and retinal vasopermeability, respectively. Hyperprolactinaemia in response to sulpiride or exogenous PRL was associated with increased levels of vasoinhibin in the retina and reduced retinal hypervasopermeability. Furthermore, sulpiride decreased retinal haemorrhages in response to the intravitreal administration of vascular endothelial growth factor (VEGF). Neither sulpiride nor exogenous PRL modified blood glucose levels or bodyweight. We conclude that sulpiride-induced hyperprolactinaemia inhibits the diabetes- and VEGF-mediated increase in retinal vasopermeability by promoting the intraocular conversion of endogenous PRL to vasoinhibin. These findings support the therapeutic potential of sulpiride and its levorotatory enantiomer, levosulpiride, against DME and DR.

The HGR motif is the antiangiogenic determinant of vasoinhibin: implications for a therapeutic orally active oligopeptide.

The hormone prolactin acquires antiangiogenic and antivasopermeability properties after undergoing proteolytic cleavage to vasoinhibin, an endogenous prolactin fragment of 123 or more amino acids that inhibits the action of multiple proangiogenic factors. Preclinical and clinical evidence supports the therapeutic potential of vasoinhibin against angiogenesis-related diseases including diabetic retinopathy, peripartum cardiomyopathy, rheumatoid arthritis, and cancer. However, the use of vasoinhibin in the clinic has been limited by difficulties in its production. Here, we removed this barrier to using vasoinhibin as a therapeutic agent by showing that a short linear motif of just three residues (His46-Gly47-Arg48) (HGR) is the functional determinant of vasoinhibin. The HGR motif is conserved throughout evolution, its mutation led to vasoinhibin loss of function, and oligopeptides containing this sequence inhibited angiogenesis and vasopermeability with the same potency as whole vasoinhibin. Furthermore, the oral administration of an optimized cyclic retro-inverse vasoinhibin heptapeptide containing HGR inhibited melanoma tumor growth and vascularization in mice and exhibited equal or higher antiangiogenic potency than other antiangiogenic molecules currently used as anti-cancer drugs in the clinic. Finally, by unveiling the mechanism that obscures the HGR motif in prolactin, we anticipate the development of vasoinhibin-specific antibodies to solve the on-going challenge of measuring endogenous vasoinhibin levels for diagnostic and interventional purposes, the design of vasoinhibin antagonists for managing insufficient angiogenesis, and the identification of putative therapeutic proteins containing HGR.

Levosulpiride Increases the Levels of Prolactin and Antiangiogenic Vasoinhibin in the Vitreous of Patients with Proliferative Diabetic Retinopathy.

Purpose: High circulating levels of the hormone prolactin (PRL) protect against experimental diabetic retinopathy (DR) due to the retinal accumulation of vasoinhibin, a PRL fragment that inhibits blood vessel permeability and growth. A phase 2 clinical trial is investigating a new therapy for DR based on elevating serum PRL levels with levosulpiride, a prokinetic dopamine D2 receptor blocker. Here, we tested whether levosulpiride-induced hyperprolactinemia elevates PRL and vasoinhibin in the vitreous of volunteer patients with proliferative DR (PDR) undergoing elective pars plana vitrectomy. Methods: Patients were randomized to receive placebo (lactose pill, orally TID; n = 19) or levosulpiride (25 mg orally TID; n = 18) for the 7 days before vitrectomy. Vitreous samples from untreated non-diabetic (n = 10) and PDR (n = 17) patients were also studied. Results: Levosulpiride elevated the systemic (101 ± 13 [SEM] vs. 9.2 ± 1.3 ng/mL, P < 0.0001) and vitreous (3.2 ± 0.4 vs. 1.5 ± 0.2 ng/mL, P < 0.0001) levels of PRL, and both levels were directly correlated (r = 0.58, P < 0.0002). The vitreous from non-diabetic patients or from PDR patients treated with levosulpiride, but not from placebo-treated PDR patients, inhibited the basic fibroblast growth factor (bFGF)- and vascular endothelial growth factor (VEGF)-induced proliferation of endothelial cells in culture. Vasoinhibin-neutralizing antibodies reduced the vitreous antiangiogenic effect. Matrix metalloproteases (MMPs) in the vitreous cleaved PRL to vasoinhibin, and their activity was higher in non-diabetic than in PDR patients. Conclusions: Levosulpiride increases the levels of PRL in the vitreous of PDR patients and promotes its MMP-mediated conversion to vasoinhibin, which can inhibit angiogenesis in DR. Translational Relevance: These findings support the potential therapeutic benefit of levosulpiride against vision loss in diabetes.