Protective effect of retinal ischemia by blockers of voltage-dependent calcium channels and intracellular calcium stores

Could dantrolene be explored as a repurposed drug to treat COVID-19 patients by restoring intracellular calcium homeostasis?

Dantrolene, an FDA approved drug to treat malignant hyperthermia and muscle spasm, has been demonstrated to inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mediated toxicity of host cells. Ryanodine receptor overactivation and associated disruption of intracellular Ca2+ homeostasis play important roles in SARS-CoV-2 infection and replication of host cells. Dantrolene, as an inhibitor of RyRs, is expected to ameliorate these detrimental effects of SARS-CoV-2 in host cells. Additionally, dantrolene has also been shown to inhibit multiple cell or organ damage induced by hypoxia/ischemia, mitochondria damage, oxidative stresses, inflammation, impairment of autophagy and apoptosis, etc., which are often the causes of severity and mortality of COVID-19 patients. We have repurposed that dantrolene has a high potential at treating COVID-19 patients and reducing its morbidity and mortality.

Ryanodine receptor antagonism alleviates skeletal muscle ischemia reperfusion injury by modulating TNF-α and IL-10

BACKGROUND

Intracellular calcium overload has been implicated in various pathological conditions including ischemia reperfusion injury. This study aims to explore the effect and probable mechanism of dantrolene, a ryanodine receptor and intracellular calcium antagonist, on the skeletal muscle ischemia reperfusion injury.

MATERIALS AND METHODS

SD rats were randomly divided into three groups: sham group which underwent anaesthesia and exposure of femoral vein, reperfusion group that received 2 h ischemia and the amount of diluent via femoral vein before 4 h reperfusion, dantrolene group that underwent 2 h ischemia and was given 2 mg/kg dantrolene via femoral vein before 4 h reperfusion. The parameters measured at the end of reperfusion included serum maleic dialdehyde (MDA), tissue myeloperoxidase (MPO) and muscle histology, as well as serum TNF-α and IL-10.

RESULTS

Levels of MDA, MPO and TNF-α increased in the reperfusion group, whereas the relevant expressions in the dantrolene group decreased significantly. Histological examination demonstrated significant improvements between the same both groups. IL-10 reflected the protection observed above with a significant up-regulation of expression after dantrolene administration.

CONCLUSION

Ryanodine receptor antagonist dantrolene exerted a significant protective effect against the inflammatory injury of skeletal muscle ischemia reperfusion. The underlying molecular mechanism is probably related to the suppression of TNF-α levels and the increment of IL-10 expression.

Synthetic Cystine-Knot Miniproteins - Valuable Scaffolds for Polypeptide Engineering

Peptides with the cystine-knot architecture, often termed knottins, are promising scaffolds for biomolecular engineering. These unique molecules combine diverse bioactivities with excellent structural, thermal, and proteolytical stability. Being different in the composition and structure of their amino acid backbone, knottins share the same core element, namely cystine knot, which is built by six cysteine residues forming three disulfides upon oxidative folding. This motif ensures a notably rigid framework that highly tolerates both rational and combinatorial changes in the primary structure. Being accessible through recombinant production and total chemical synthesis, cystine-knot miniproteins can be endowed with novel bioactivities by variation of surface-exposed loops and incorporation of non-natural elements within their non-conserved regions towards the generation of tailor-made peptidic compounds. In this chapter the topology of cystine-knot peptides, their synthesis and applications for diagnostics and therapy is discussed.

MRI biomarkers for evaluation of treatment efficacy in preclinical diabetic retinopathy

INTRODUCTION

One sober consequence of the current epidemic of diabetes mellitus is that an increasing number of people world-wide will partially or completely lose their sight to diabetic retinopathy. Clinically, the sight-threatening complications of diabetes are diagnosed and treated based on visible retinal lesions (e.g., dot-blot hemorrhages or retinal neovascularization). However, such anatomical microvascular lesions are slow to respond with treatment. Thus, there remains an urgent need for imaging biomarkers that are abnormal before retinal lesions are visibly apparent and are responsive to treatment.

AREAS COVERED

Here, the development of new MRI methods, such as manganese-enhanced MRI, for evaluating early diabetes-evoked retinal pathophysiology, and its usefulness in guiding new treatments for diabetic retinopathy are reviewed.

EXPERT OPINION

In diabetic retinopathy, not all important diagnostic and prognostic needs are well served by optical methods. In the absence of gross anatomy changes, critical times when drug intervention is most likely to be successful at reducing vision loss are missed by most light-based methods and thus provide little help in guiding diagnosis and treatment. For example, before clinical symptoms, is there an optimal time to intervene with drug therapy? Is a drug reaching its target? How does one assess optimal drug dose, schedule, and routes? How well do current experimental models mimic the clinical condition? As discussed herein, MRI is as an analytical tool for addressing these unmet needs. Future clinical applications of MRI can be envisioned such as in clinical trials to assess drug treatment efficacy, or as an adjunct approach to refine or clarify a difficult clinical case. New MRI-generated hypotheses about the pathogenesis of diabetic retinopathy and its treatment are discussed. In the coming years, a substantial growth in the development and application of MRI is expected to address relevant question in both the basic sciences and in the clinic.

Recent advances in cellular and molecular aspects of mammalian retinal ischemia

Retinal ischemia is a common clinical entity and, due to relatively ineffective treatment, remains a common cause of visual impairment and blindness. Generally, ischemic syndromes are initially characterized by low homeostatic responses which, with time, induce injury to the tissue due to cell loss by apoptosis. In this respect, retinal ischemia is a primary cause of neuronal death. It can be considered as a sort of final common pathway in retinal diseases and results in irreversible morphological and functional changes. This review summarizes the recent knowledge on the effects of ischemia in retinal tissue and points out experimental strategies/models performed to gain better comprehension of retinal ischemia diseases. In particular, the nature of the mechanisms leading to neuronal damage (i.e., excess of glutamate release, oxidative stress and inflammation) will be outlined as well as the potential and most intriguing retinoprotective approaches and the possible therapeutic use of naturally occurring molecules such as neuropeptides. There is a general agreement that a better understanding of the fundamental pathophysiology of retinal ischemia will lead to better management and improved clinical outcome. In this respect, to contrast this pathological state, specific pharmacological strategies need to be developed aimed at the many putative cascades generated during ischemia.

Engineered cystine-knot miniproteins for diagnostic applications

Owing to their extraordinary thermal and biological stability, cystine-knot miniproteins provide an attractive scaffold for the development of peptide-based diagnostics. One of the major advantages of this scaffold lies in the fact that the disulfide-constrained structural core can be functionalized by decoration with bioactive-loop residues. Methods have been developed to generate miniproteins with prescribed binding characteristics to a broad spectrum of different target proteins. They combine structural, biophysical and functional features that are beneficial for applications in molecular diagnostics in vivo (i.e., high affinity and selectivity, small size, high biological stability and fast renal clearance). Promising candidates for tumor imaging have been generated recently and evaluated in animal models, and more applications are expected in the near future.

Dantrolene: mechanisms of neuroprotection and possible clinical applications in the neurointensive care unit

Calcium plays a central role in neuronal function and injury. Dantrolene, an inhibitor of the ryanodine receptor, inhibits intracellular calcium release from the sarco-endoplasmic reticulum. We review the available data of dantrolene as a potential neuroprotective agent and briefly summarize its other pharmacologic effects that may have potential applications for patients in the neurointensive care unit (NICU). Areas with the need for continued research are identified.