Smoothened-antagonists reverse homogentisic acid-induced alterations of Hedgehog signaling and primary cilium length in alkaptonuria

Alkaptonuria

Alkaptonuria is a rare inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase activity. The consequent homogentisic acid (HGA) accumulation in body fluids and tissues leads to a multisystemic and highly debilitating disease whose main features are dark urine, ochronosis (HGA-derived pigment in collagen-rich connective tissues), and a painful and severe form of osteoarthropathy. Other clinical manifestations are extremely variable and include kidney and prostate stones, aortic stenosis, bone fractures, and tendon, ligament and/or muscle ruptures. As an autosomal recessive disorder, alkaptonuria affects men and women equally. Debilitating symptoms appear around the third decade of life, but a proper and timely diagnosis is often delayed due to their non-specific nature and a lack of knowledge among physicians. In later stages, patients' quality of life might be seriously compromised and further complicated by comorbidities. Thus, appropriate management of alkaptonuria requires a multidisciplinary approach, and periodic clinical evaluation is advised to monitor disease progression, complications and/or comorbidities, and to enable prompt intervention. Treatment options are patient-tailored and include a combination of medications, physical therapy and surgery. Current basic and clinical research focuses on improving patient management and developing innovative therapies and implementing precision medicine strategies.

Ochronotic Chondropathy: A Case Report

Endogenous ochronosis, also known as alkaptonuria, is a rare disease known for its bluish-black discoloration of the skin, sclerae, and pinnae, as well as urine that turns black upon standing. Though rarely fatal, joint degradation is a common sequela, and many patients require multiple large joint arthroplasties throughout their lifetime. Though many aspects of the pathophysiological mechanisms of the disease have been described, questions remain, such as how the initiation of ochronotic pigmentation is prompted and the specific circumstances that make some tissues more resistant to pigmentation-related damage than others. In this report, we present the case of an 83-year-old female previously diagnosed with alkaptonuria including high-quality arthroscopic images displaying the fraying of articular cartilage. We also offer a summary of the latest literature on the pathophysiological mechanisms of the disease, including cellular-level changes observed in ochronotic chondrocytes, biochemical and mechanical alterations to the cartilaginous extracellular matrix, and patterns of pigmentation and joint degradation observed in humans and mice models. With these, we present an overview of the mechanisms of ochronotic chondropathy and joint degradation as the processes are currently understood. While alkaptonuria itself is rare, it has been termed a "fundamental disease," implying that its study and greater understanding have the potential to lead to insights in skeletal biology in general, as well as more common pathologies such as osteoarthritis and their potential treatment mechanisms.

Antiangiogenic Effect of Dopamine and Dopaminergic Agonists as an Adjuvant Therapeutic Option in the Treatment of Cancer, Endometriosis, and Osteoarthritis

Dopamine (DA) and dopamine agonists (DA-Ag) have shown antiangiogenic potential through the vascular endothelial growth factor (VEGF) pathway. They inhibit VEGF and VEGF receptor 2 (VEGFR 2) functions through the dopamine receptor D2 (D2R), preventing important angiogenesis-related processes such as proliferation, migration, and vascular permeability. However, few studies have demonstrated the antiangiogenic mechanism and efficacy of DA and DA-Ag in diseases such as cancer, endometriosis, and osteoarthritis (OA). Therefore, the objective of this review was to describe the mechanisms of the antiangiogenic action of the DA-D2R/VEGF-VEGFR 2 system and to compile related findings from experimental studies and clinical trials on cancer, endometriosis, and OA. Advanced searches were performed in PubMed, Web of Science, SciFinder, ProQuest, EBSCO, Scopus, Science Direct, Google Scholar, PubChem, NCBI Bookshelf, DrugBank, livertox, and Clinical Trials. Articles explaining the antiangiogenic effect of DA and DA-Ag in research articles, meta-analyses, books, reviews, databases, and clinical trials were considered. DA and DA-Ag have an antiangiogenic effect that could reinforce the treatment of diseases that do not yet have a fully curative treatment, such as cancer, endometriosis, and OA. In addition, DA and DA-Ag could present advantages over other angiogenic inhibitors, such as monoclonal antibodies.

Identification of Potential Inhibitors for the Treatment of Alkaptonuria Using an Integrated In Silico Computational Strategy

Alkaptonuria (AKU) is a rare genetic autosomal recessive disorder characterized by elevated serum levels of homogentisic acid (HGA). In this disease, tyrosine metabolism is interrupted because of the alterations in homogentisate dioxygenase (HGD) gene. The patient suffers from ochronosis, fractures, and tendon ruptures. To date, no medicine has been approved for the treatment of AKU. However, physiotherapy and strong painkillers are administered to help mitigate the condition. Recently, nitisinone, an FDA-approved drug for type 1 tyrosinemia, has been given to AKU patients in some countries and has shown encouraging results in reducing the disease progression. However, this drug is not the targeted treatment for AKU, and causes keratopathy. Therefore, the foremost aim of this study is the identification of potent and druggable inhibitors of AKU with no or minimal side effects by targeting 4-hydroxyphenylpyruvate dioxygenase. To achieve our goal, we have performed computational modelling using BioSolveIT suit. The library of ligands for molecular docking was acquired by fragment replacement of reference molecules by ReCore. Subsequently, the hits were screened on the basis of estimated affinities, and their pharmacokinetic properties were evaluated using SwissADME. Afterward, the interactions between target and ligands were investigated using Discovery Studio. Ultimately, compounds c and f were identified as potent inhibitors of 4-hydroxyphenylpyruvate dioxygenase.

Effects of Nitisinone on Oxidative and Inflammatory Markers in Alkaptonuria: Results from SONIA1 and SONIA2 Studies

Nitisinone (NTBC) was recently approved to treat alkaptonuria (AKU), but there is no information on its impact on oxidative stress and inflammation, which are observed in AKU. Therefore, serum samples collected during the clinical studies SONIA1 (40 AKU patients) and SONIA2 (138 AKU patients) were tested for Serum Amyloid A (SAA), CRP and IL-8 by ELISA; Advanced Oxidation Protein Products (AOPP) by spectrophotometry; and protein carbonyls by Western blot. Our results show that NTBC had no significant effects on the tested markers except for a slight but statistically significant effect for NTBC, but not for the combination of time and NTBC, on SAA levels in SONIA2 patients. Notably, the majority of SONIA2 patients presented with SAA > 10 mg/L, and 30 patients in the control group (43.5%) and 40 patients (58.0%) in the NTBC-treated group showed persistently elevated SAA > 10 mg/L at each visit during SONIA2. Higher serum SAA correlated with lower quality of life and higher morbidity. Despite no quantitative differences in AOPP, the preliminary analysis of protein carbonyls highlighted patterns that deserve further investigation. Overall, our results suggest that NTBC cannot control the sub-clinical inflammation due to increased SAA observed in AKU, which is also a risk factor for developing secondary amyloidosis.

Leveraging proteomics in orphan disease research: pitfalls and potential

Introduction: The term 'orphan diseases' includes conditions meeting prevalence-based or commercial viability criteria: they affect a small number of individuals and are considered an unviable market for drug development. Proteomics is an important technology to study them, providing information on mechanisms and evolution, biomarkers, and effects of therapeutic interventions.Areas covered: Herein, we review how proteomics and bioinformatic tools could be applied to the study of rare diseases and discuss pitfalls and potential.Expert opinion: Research in the field of rare diseases has to face many challenges, and implementation plans should foresee highly specialized collaborative consortia to create multidisciplinary frameworks for data sharing, advancing research, supporting clinical studies, and accelerating drug development. The integration of different technologies will allow better knowledge of disease pathophysiology, and the inclusion of proteomics and other omics technologies in this context will be pivotal to this aim.Several aspects of rare diseases, often perceived as limiting factors, might actually be advantages for a precision medicine approach: the limited number of patients, the collaboration with patient societies, and the availability of curated clinical registries could allow the development of homogeneous clinical databases and ultimately a better control over the data to be analyzed.

Homogentisic acid induces cytoskeleton and extracellular matrix alteration in alkaptonuric cartilage

Alkaptonuria (AKU) is an ultra-rare disease caused by the deficient activity of homogentisate 1,2-dioxygenase enzyme, leading the accumulation of homogentisic acid (HGA) in connective tissues implicating the formation of a black pigmentation called "ochronosis." Although AKU is a multisystemic disease, the most affected tissue is the articular cartilage, which during the pathology appears to be highly damaged. In this study, a model of alkaptonuric chondrocytes and cartilage was realized to investigate the role of HGA in the alteration of the extracellular matrix (ECM). The AKU tissues lost its architecture composed of collagen, proteoglycans, and all the proteins that characterize the ECM. The cause of this alteration in AKU cartilage is attributed to a degeneration of the cytoskeletal network in chondrocytes caused by the accumulation of HGA. The three cytoskeletal proteins, actin, vimentin, and tubulin, were analyzed and a modification in their amount and disposition in AKU chondrocytes model was identified. Cytoskeleton is involved in many fundamental cellular processes; therefore, the aberration in this complex network is involved in the manifestation of AKU disease.

Ciliary IFT80 is essential for intervertebral disc development and maintenance

The intervertebral disc degeneration (IVDD)-related diseases occur in more than 90% of the population older than 50 years. Owing to the lack of understanding of the cellular mechanisms involved in IVDD formation effective treatment options are still unavailable. Primary cilia are microtubule-based organelles that play important roles in the organ development. Intraflagellar transport (IFT) proteins are essential for the assembly and bidirectional transport within the cilium. Role of cilia and IFT80 protein in intervertebral disc (IVD) development, maintenance, and degeneration are largely unknown. Using cilia-GFP mice, we found presence of cilia on growth plate (GP), cartilage endplate (EP) annulus fibrosus (AF), and nucleus pulposus (NP) with varying ciliary length. Cilia length in NP and AF during IVDD were significantly decreased. However, cilia numbers increased by 63% in AF during repair. Deletion of IFT80 in type II collagen-positive cells resulted in cilia loss in GP and EP, and disrupted IVD structure with disorganized and decreased GP, EP, and internal AF (IAF), and less compact and markedly decreased gel-like matrix in the NP. Deletion of IFT80 in type I collagen-positive cells led to a disorganized outer AF (OAF) with thinner, loosened, and disconnected fiber alignment. Mechanistic analyses showed that loss of IFT80 caused a significant increase in cell apoptosis in the IVD, and a marked decrease in expression of chondrogenic markers - type II collagen, sox9, aggrecan, and hedgehog (Hh) signaling components, including Gli1 and Patch1 in the IVD of IFT80^fl/fl ; Col2-creERT mice, and Gli1 and Patch1 expression in the OAF of IFT80^fl/fl ; Col1-creERT mice. Interestingly, Smoothened agonist-SAG rescued OAF cell proliferation and osteogenic differentiation. Our findings demonstrate that ciliary IFT80 is important for the maintenance of IVD cell organization and function through regulating the cell survival and Hh signaling.

Primary cilia: Versatile regulator in cartilage development

Cartilage is a connective tissue in the skeletal system and has limited regeneration ability and unique biomechanical reactivity. The growth and development of cartilage can be affected by different physical, chemical and biological factors, such as mechanical stress, inflammation, osmotic pressure, hypoxia and signalling transduction. Primary cilia are multifunctional sensory organelles that regulate diverse signalling transduction and cell activities. They are crucial for the regulation of cartilage development and act in a variety of ways, such as react to mechanical stress, mediate signalling transduction, regulate cartilage‐related diseases progression and affect cartilage tumorigenesis. Therefore, research on primary cilia‐mediated cartilage growth and development is currently extremely popular. This review outlines the role of primary cilia in cartilage development in recent years and elaborates on the potential regulatory mechanisms from different aspects.

Functional role of hedgehog pathway in osteoarthritis

The hedgehog signalling pathway is one of the key regulators of metazoan development, and it plays an important role in the regulation of a variety of developmental and physiological processes. But it is aberrantly activated in many human diseases, including osteoarthritis (OA). In this study, we have reviewed the association of hedgehog signalling pathway in the development and progression of OA and evaluated the efforts to target this pathway for the prevention of OA. Usually in OA, activation of hedgehog induces up-regulation of the expression of hypertrophic markers, including type X collagen, increases production of nitric oxide and prostaglandin E2, several matrix-degrading enzymes including matrix metalloproteinase and a disintegrin and metalloproteinase with thrombospondin motifs in human knee joint cartilage leading to cartilage degeneration, and thus contributes in OA. Targeting hedgehog signalling might be a viable strategy to prevent or treat OA. Chemical inhibitors of hedgehog signalling is promising, but they cause severe side effects. Knockdown of HH gene is not an option for OA treatment in humans because it is not possible to delete HH in larger animals. Efficient knockdown of HH achieved by local delivery of small interfering RNA in future studies utilizing large animal OA models might be a more efficient approach for the prevention of OA. However, it remains a major problem to develop one single scaffold due to the different physiological functions of cartilage and subchondral bones possess. More studies are necessary to identify selective inhibitors for efficiently targeting the hedgehog pathway in clinical conditions.

Inflammatory and oxidative stress biomarkers in alkaptonuria: data from the DevelopAKUre project

OBJECTIVE

The aim of this work was to assess baseline serum levels of established biomarkers related to inflammation and oxidative stress in samples from alkaptonuric subjects enrolled in SONIA1 (n = 40) and SONIA2 (n = 138) clinical trials (DevelopAKUre project).

METHODS

Baseline serum levels of Serum Amyloid A (SAA), IL-6, IL-1β, TNFα, CRP, cathepsin D (CATD), IL-1ra, and MMP-3 were determined through commercial ELISA assays. Chitotriosidase activity was assessed through a fluorimetric method. Advanced Oxidation Protein Products (AOPP) were determined by spectrophotometry. Thiols, S-thiolated proteins and Protein Thiolation Index (PTI) were determined by spectrophotometry and HPLC. Patients' quality of life was assessed through validated questionnaires.

RESULTS

We found that SAA serum levels were significantly increased compared to reference threshold in 57.5% and 86% of SONIA1 and SONIA2 samples, respectively. Similarly, chitotriosidase activity was above the reference threshold in half of SONIA2 samples, whereas CRP levels were increased only in a minority of samples. CATD, IL-1β, IL-6, TNFα, MMP-3, AOPP, thiols, S-thiolated protein and PTI showed no statistically significant differences from control population. We provided evidence that alkaptonuric patients presenting with significantly higher SAA, chitotriosidase activity and PTI reported more often a decreased quality of life. This suggests that worsening of symptoms in alkaptonuria (AKU) is paralleled by increased inflammation and oxidative stress, which might play a role in disease progression.

CONCLUSIONS

Monitoring of SAA may be suggested in AKU to evaluate inflammation. Though further evidence is needed, SAA, chitotriosidase activity and PTI might be proposed as disease activity markers in AKU.

Hedgehog pathway inhibitors of the acylthiourea and acylguanidine class show antitumor activity on colon cancer in vitro and in vivo

Small series of acylguanidine and acylthiourea derivatives were synthesized in gram-scale and assayed for their ability to modulate the Hh signalling pathway. In vitro studies showed a low micromolar inhibitory activity toward tumor cell lines, while the oral administration revealed an excellent ADME profile in vivo. Compound 5 emerged as the most active and safe inhibitor of colon cancer cells both in vitro and in a xenograft mouse model. Based on these data, 5 could be prioritized to further development with the perspective of clinical studies.

Novel smoothened antagonists as anti-neoplastic agents for the treatment of osteosarcoma

Osteosarcoma (OS) is an ultra-rare highly malignant tumor of the skeletal system affecting mainly children and young adults and it is characterized by an extremely aggressive clinical course. OS patients are currently treated with chemotherapy and complete surgical resection of cancer tissue. However, resistance to chemotherapy and the recurrence of disease, as pulmonary metastasis, remain the two greatest challenges in the management, and treatment of this tumor. For these reasons, it is of primary interest to find alternative therapeutic strategies for OS. Dysregulated Hedgehog signalling is involved in the development of various types of cancers including OS. It has also been implicated in tumor/stromal interaction and cancer stem cell biology, and therefore presents a novel therapeutic strategy for cancer treatment. In our work, we tested the activity of five potent Smoothened (SMO) inhibitors, four acylguanidine and one acylthiourea derivatives, against an OS cell line. We found that almost all our compounds were able to inhibit OS cells proliferation and to reduce Gli1 protein levels. Our results also indicated that SMO inhibition in OS cells by such compounds, induces apoptosis with a nanomolar potency. These findings suggest that inactivation of SMO may be a useful approach to the treatment of patients with OS.