Sphingosine 1-phosphate accelerates wound healing in diabetic mice

Bioinformatics to Identify Biomarkers of Diabetic Nephropathy based on Sphingolipid Metabolism and their Molecular Mechanisms

BACKGROUND

Diabetes mellitus (DM) frequently results in Diabetic Nephropathy (DN), which has a significant negative impact on the quality of life of diabetic patients. Sphingolipid metabolism is associated with diabetes, but its relationship with DN is unclear. Therefore, screening biomarkers related to sphingolipid metabolism is crucial for treating DN.

METHODS

To identify Differentially Expressed Genes (DEGs) in the GSE142153 dataset, we conducted a differential expression analysis (DN samples versus control samples). The intersection genes were obtained by overlapping DEGs and Sphingolipid Metabolism-Related Genes (SMRGs). Furthermore, The Least Absolute Shrinkage and Selection Operator (LASSO) and Support Vector Machine Recursive Feature Elimination (SVM-RFE) algorithms were used to filter biomarkers. We further analyzed the Gene Set Enrichment analysis (GSEA) and the immunoinfiltrational analysis based on biomarkers.

RESULTS

We identified 2,186 DEGs associated with DN. Then, five SMR-DEGs were obtained. Subsequently, biomarkers associated with sphingolipid metabolism (S1PR1 and SELL) were identified by applying machine learning and expression analysis. In addition, GSEA showed that these biomarkers were correlated with cytokine cytokine receptor interaction'. Significant variations in B cells, DCs, Tems, and Th2 cells between the two groups suggested that these cells might have a role in DN.

CONCLUSION

Overall, we obtained two sphingolipid metabolism-related biomarkers (S1PR1 and SELL) associated with DN, which laid a theoretical foundation for treating DN.

Fingolimod Alleviates Cognitive Deficit in Type 2 Diabetes by Promoting Microglial M2 Polarization via the pSTAT3-jmjd3 Axis

Sphingosine receptors (S1PRs) are implicated in the progression of neurodegenerative diseases and metabolic disorders like obesity and type 2 diabetes (T2D). The link between S1PRs and cognition in type 2 diabetes, as well as the mechanisms that underpin it, are yet unknown. Neuroinflammation is the common pathology shared among T2D and cognitive impairment. However, the interplay between the M1 and M2 polarization state of microglia, a primary driver of neuroinflammation, could be the driving factor for impaired learning and memory in diabetes. In the present study, we investigated the effects of fingolimod (S1PR1 modulator) on cognition in high-fat diet and streptozotocin-induced diabetic mice. We further assessed the potential pathways linking microglial polarization and cognition in T2D. Fingolimod (0.5 mg/kg and 1 mg/kg) improved M2 polarization and synaptic plasticity while ameliorating cognitive decline and neuroinflammation. Sphingolipid dysregulation was mimicked in vitro using palmitate in BV2 cells, followed by conditioned media exposure to Neuro2A cells. Mechanistically, type 2 diabetes induced microglial activation, priming microglia towards the M1 phenotype. In the hippocampus and cortex of type 2 diabetic mice, there was a substantial drop in pSTAT3, which was reversed by fingolimod. This protective effect of fingolimod on microglial M2 polarization was primarily suppressed by selective jmjd3 blockade in vitro using GSK-J4, revealing that jmjd3 was involved downstream of STAT3 in the fingolimod-enabled shift of microglia from M1 to M2 polarization state. This study suggested that fingolimod might effectively improve cognition in type 2 diabetes by promoting M2 polarization.

Limited Treatment Options for Diabetic Wounds: Barriers to Clinical Translation Despite Therapeutic Success in Murine Models

Significance: Millions of people worldwide suffer from diabetes mellitus and its complications, including chronic diabetic wounds. To date, there are few widely successful clinical therapies specific to diabetic wounds beyond general wound care, despite the vast number of scientific discoveries in the pathogenesis of defective healing in diabetes. Recent Advances: In recent years, murine animal models of diabetes have enabled the investigation of many possible therapeutics for diabetic wound care. These include specific cell types, growth factors, cytokines, peptides, small molecules, plant extracts, microRNAs, extracellular vesicles, novel wound dressings, mechanical interventions, bioengineered materials, and more. Critical Issues: Despite many research discoveries, few have been translated from their success in murine models to clinical use in humans. This massive gap between bench discovery and bedside application begs the simple and critical question: what is still missing? The complexity and multiplicity of the diabetic wound makes it an immensely challenging therapeutic target, and this lopsided progress highlights the need for new methods to overcome the bench-to-bedside barrier. How can laboratory discoveries in animal models be effectively translated to novel clinical therapies for human patients? Future Directions: As research continues to decipher deficient healing in diabetes, new approaches and considerations are required to ensure that these discoveries can become translational, clinically usable therapies. Clinical progress requires the development of new, more accurate models of the human disease state, multifaceted investigations that address multiple critical components in wound repair, and more innovative research strategies that harness both the existing knowledge and the potential of new advances across disciplines.

The role of lipid-based signalling in wound healing and senescence

Lipid-based signalling modulates several cellular processes and intercellular communication during wound healing and tissue regeneration. Bioactive lipids include but are not limited to the diverse group of eicosanoids, phospholipids, and extracellular vesicles and mediate the attraction of immune cells, initiation of inflammatory responses, and their resolution. In aged individuals, wound healing and tissue regeneration are greatly impaired, resulting in a delayed healing process and non-healing wounds. Senescent cells accumulate with age in vivo, preferably at sites implicated in age-associated pathologies and their elimination was shown to alleviate many age-associated diseases and disorders. In contrast to these findings, the transient presence of senescent cells in the process of wound healing exerts beneficial effects and limits fibrosis. Hence, clearance of senescent cells during wound healing was repeatedly shown to delay wound closure in vivo. Recent findings established a dysregulated synthesis of eicosanoids, phospholipids and extracellular vesicles as part of the senescent phenotype. This intriguing connection between cellular senescence, lipid-based signalling, and the process of wound healing and tissue regeneration prompts us to compile the current knowledge in this review and propose future directions for investigation.

Beyond Growth Factors: Macrophage-Centric Strategies for Angiogenesis

Functional angiogenesis is a critical therapeutic goal in many pathological conditions. Logically, the use of pro-angiogenic growth factors has been the mainstay approach despite obvious limitations and modest success. Recently, macrophages have been identified as key regulators of the host response to implanted materials. Particularly, our understanding of dynamically plastic macrophage phenotypes, their interactions with biomaterials, and varied roles in different stages of angiogenic processes is evolving rapidly. In this review, we discuss changing perspectives on therapeutic angiogenesis, in relation to implantable materials and macrophage-centric strategies therein. Harnessing the different mechanisms through which the macrophage-driven host response is involved in angiogenesis has great potential for improving clinical outcome.

MYPT1 O-GlcNAc modification regulates sphingosine-1-phosphate mediated contraction

Many intracellular proteins are modified by N-acetylglucosamine, a posttranslational modification termed O-GlcNAc. This modification is found on serine and threonine side-chains and has the potential to regulate signaling pathways through interplay with phosphorylation. Here, we discover and characterize one such example. We find that O-GlcNAc levels control the sensitivity of fibroblasts to actin contraction induced by the signaling lipid sphingosine-1-phosphate (S1P), culminating in the phosphorylation of myosin light chain (MLC) and cellular contraction. Specifically, O-GlcNAc modification of the phosphatase subunit MYPT1 inhibits this pathway by blocking MYPT1 phosphorylation, maintaining its activity and causing the dephosphorylation of MLC. Finally, we demonstrate that O-GlcNAc levels alter the sensitivity of primary human dermal fibroblasts in a collagen-matrix model of wound healing. Our findings have important implications for the role of O-GlcNAc in fibroblast motility and differentiation, particularly in diabetic wound healing.

Mechanistic insight into diabetic wounds: Pathogenesis, molecular targets and treatment strategies to pace wound healing

Wound management in diabetic patient is of an extreme clinical and social concern. The delayed and impaired healing makes it more critical for research focus. The research on impaired healing process is proceeding hastily evident by new therapeutic approaches other than conventional such as single growth factor, dual growth factor, skin substitutes, cytokine stimulators, cytokine inhibitors, matrix metalloproteinase inhibitors, gene and stem cell therapy, extracellular matrix and angiogenesis stimulators. Although numerous studies are available that support delayed wound healing in diabetes but detailed mechanistic insight including factors involved and their role still needs to be revealed. This review mainly focuses on the molecular cascades of cytokines (with growth factors) and erstwhile factors responsible for delayed wound healing, molecular targets and recent advancements in complete healing and its cure. Present article briefed recent pioneering information on possible molecular targets and treatment strategies including clinical trials to clinicians and researchers working in similar area.

Emergence of membrane sphingolipids as a potential therapeutic target

BACKGROUND

Though sphingolipids are ubiquitously present in eukaryotic cells, but until the last decade, they were merely considered as a structural component of the plasma membrane with limited function. However, over the last decade, numerous functions have been ascribed to sphingolipids after the seminal discoveries on the bioactivities of several sphingolipids.

SCOPE OF REVIEW

Sphingolipids are now well-recognized signals for fundamental cellular processes. Here we discussed about the advent of several sphingolipids components as potential therapeutic target for both human and plants.

MAJOR CONCLUSIONS

Sphingolipid contents and/or sphingolipid-metabolizing enzyme expression/activity often get impaired during pathophysiological conditions, and hence manipulation of this signaling pathway may be beneficial in disease diagnosis, and the plasma concentrations can serve as an important prognostic and diagnostic marker for the disease.

GENERAL SIGNIFICANCE

Sphingolipids are emerging as a goldmine for new therapeutic drug targets with promising new applications (cosmeceutical and nutraceutical), thereby opening new avenues for pharmaceuticals and nutraceutical industries.

Induction of hemangiosarcoma in mice after chronic treatment with S1P-modulator siponimod and its lack of relevance to rat and human

A high incidence of hemangiosarcoma (HSA) was observed in mice treated for 2 years with siponimod, a sphingosine-1-phosphate receptor 1 (S1P1) functional antagonist, while no such tumors were observed in rats under the same treatment conditions. In 3-month rat (90 mg/kg/day) and 9-month mouse (25 and 75 mg/kg/day) in vivo mechanistic studies, vascular endothelial cell (VEC) activation was observed in both species, but VEC proliferation and persistent increases in circulating placental growth factor 2 (PLGF2) were only seen in the mouse. In mice, these effects were sustained over the 9-month study duration, while in rats increased mitotic gene expression was present at day 3 only and PLGF2 was induced only during the first week of treatment. In the mouse, the persistent VEC activation, mitosis induction, and PLGF2 stimulation likely led to sustained neo-angiogenesis which over life-long treatment may result in HSA formation. In rats, despite sustained VEC activation, the transient mitotic and PLGF2 stimuli did not result in the formation of HSA. In vitro, the mouse and rat primary endothelial cell cultures mirrored their respective in vivo findings for cell proliferation and PLGF2 release. Human VECs, like rat cells, were unresponsive to siponimod treatment with no proliferative response and no release of PLGF2 at all tested concentrations. Hence, it is suggested that the human cells also reproduce a lack of in vivo response to siponimod. In conclusion, the molecular mechanisms leading to siponimod-induced HSA in mice are considered species specific and likely irrelevant to humans.

Complete metabolome and lipidome analysis reveals novel biomarkers in the human diabetic corneal stroma

Prolonged hyperglycemia during diabetes mellitus can cause severe ophthalmic complications affecting both the anterior and posterior ocular segments leading to impaired vision or blindness. Diabetes-induced corneal pathologies are associated with decreased wound healing capacity, corneal edema, and altered epithelial basement membrane. The mechanism by which diabetes modulates structure and function within the corneal stroma are unknown. In our study, we characterized the effects of diabetes on extracellular matrix, lipid transport, and cellular metabolism by defining the entire metabolome and lipidome of Type 1 and Type 2 human diabetic corneal stroma. Significant increases in Collagen I and III were found in diabetic corneas suggesting that diabetes promotes defects in matrix structure leading to scarring. Furthermore, increased lipid content, including sphingosine-1-phosphate and dihydrosphingosine, in diabetic corneas compared to healthy controls were measured suggesting altered lipid retention. Metabolomics analysis identified elevated tryptophan metabolites, independent of glucose metabolism, which correlated with upregulation of the Kynurenine pathway in diabetic corneas. We also found significant upregulation of novel biomarkers aminoadipic acid, D,L-pipecolic acid, and dihydroorotate. Our study links aberrant tryptophan metabolism to end-stage pathologies associated with diabetes indicating the potential of the Kynurenine pathway as a therapeutic target for inhibiting diabetes-associated defects in the eye.

Sphingosine 1-phosphate in metabolic syndrome (Review)

Metabolic syndrome (MetS), a clustering of components, is closely associated with the development and prognosis of cardiovascular disease and diabetes. Sphingosine 1-phosphate (S1P) is a lysophospholipid with paracrine and autocrine effects, which is associated with obesity, insulin resistance, hyperglycemia, dyslipidemia and hypertension through extracellular and intracellular signals to achieve a variety of biological functions. However, there is controversy regarding the role of S1P in MetS; the specific role played by S1P remains unclear. It ameliorates abnormal energy metabolism and deviant adipogenesis and mediates inflammation in obesity. Despite the fact that sphingosine kinase (SphK)2/S1P increases the glucose‑stimulated insulin secretion of β-cells, more evidence showed that activation of the SphK1/S1P/S1P2R pathway inhibited the feedback loop of insulin secretion and sensitivity. The majority of S1P1R activation improves diabetes whereas S1P2R activation worsens the condition. In hyperlipidemia, S1P binds to high-density lipoprotein, low‑density lipoprotein and very low-density lipoprotein exerting different effects. Moreover, low concentrations of S1P lead to vasodilation whereas high concentrations of S1P result in vasocontraction of isolated arterioles. This review discusses the means by which different SphKs, S1P concentrations or S1P receptor subtypes results to diverse result in MetS, and then examines the role of S1P in MetS.

ABCG2 deficiency in skin impairs re-epithelialization in cutaneous wound healing

The ATP-binding cassette transporter ABCG2 is expressed in the interfollicular epidermis and mediates the side-population phenotype in skin cells. However, the role of ABCG2 in skin is unclear. Increased expression levels of ABCG2 were found at the basal layer of transitional epidermis adjacent to cutaneous wounds in human patients, indicating that ABCG2 may be involved in regulating the wound healing process. To investigate the role of ABCG2 in cutaneous wound healing, full-thickness skin wounds were created in ABCG2 knockout (ABCG2-KO) and wild-type mice. The healing process was analysed and revealed that ABCG2 deficiency in skin results in delays in wound closure and impairments in re-epithelialization, as evidenced by reductions in both suprabasal differentiation and in p63-expressing keratinocytes migrating from transitional epidermis to epithelial tongues. The reduction in p63-expressing cells may be due to elevated levels of reactive oxygen species in ABCG2-KO epidermis, which can cause DNA damage and lead to proliferation arrest. To determine whether ABCG2 deficiency affects the potency of epidermal stem/progenitor cells (EPCs), transplantation studies were carried out, which demonstrated that ABCG2-KO EPCs display higher levels of γH2AX and lose the capacity to differentiate into suprabasal keratinocytes. A competitive repopulation assay confirmed that ABCG2 expression is critical for the proper expansion and differentiation of EPCs in cutaneous wounds. As EPCs are known to contribute to the healing of larger wounds, the current findings imply a functional role for ABCG2 in the expansion and differentiation of p63-expressing EPCs. Thus, ABCG2 deficiency in skin impairs re-epithelialization in cutaneous wound healing.

Biodegradable PEG-Based Amphiphilic Block Copolymers for Tissue Engineering Applications

Biodegradable tissue engineering scaffolds have great potential for delivering cells/therapeutics and supporting tissue formation. Polyesters, the most extensively investigated biodegradable synthetic polymers, are not ideally suited for diverse tissue engineering applications due to limitations associated with their hydrophobicity. This review discusses the design and applications of amphiphilic block copolymer scaffolds integrating hydrophilic poly(ethylene glycol) (PEG) blocks with hydrophobic polyesters. Specifically, we highlight how the addition of PEG results in striking changes to the physical properties (swelling, degradation, mechanical, handling) and biological performance (protein & cell adhesion) of the degradable synthetic scaffolds in vitro. We then perform a critical review of how these in vitro characteristics translate to the performance of biodegradable amphiphilic block copolymer-based scaffolds in the repair of a variety of tissues in vivo including bone, cartilage, skin, and spinal cord/nerve. We conclude the review with recommendations for future optimizations in amphiphilic block copolymer design and the need for better-controlled in vivo studies to reveal the true benefits of the amphiphilic synthetic tissue scaffolds.

Engineering in vivo gradients of sphingosine-1-phosphate receptor ligands for localized microvascular remodeling and inflammatory cell positioning

Biomaterial-mediated controlled release of soluble signaling molecules is a tissue engineering approach to spatially control processes of inflammation, microvascular remodeling and host cell recruitment, and to generate biochemical gradients in vivo. Lipid mediators, such as sphingosine 1-phosphate (S1P), are recognized for their essential roles in spatial guidance, signaling and highly regulated endogenous gradients. S1P and pharmacological analogs such as FTY720 are therapeutically attractive targets for their critical roles in the trafficking of cells between blood and tissue spaces, both physiologically and pathophysiologically. However, the interaction of locally delivered sphingolipids with the complex metabolic networks controlling the flux of lipid species in inflamed tissue has yet to be elucidated. In this study, complementary in vitro and in vivo approaches are investigated to identify relationships between polymer composition, drug release kinetics, S1P metabolic activity, signaling gradients and spatial positioning of circulating cells around poly(lactic-co-glycolic acid) biomaterials. Results demonstrate that biomaterial-based gradients of S1P are short-lived in the tissue due to degradation by S1P lyase, an enzyme that irreversibly degrades intracellular S1P. On the other hand, in vivo gradients of the more stable compound, FTY720, enhance microvascular remodeling by selectively recruiting an anti-inflammatory subset of monocytes (S1P3(high)) to the biomaterial. Results highlight the need to better understand the endogenous balance of lipid import/export machinery and lipid kinase/phosphatase activity in order to design biomaterial products that spatially control the innate immune environment to maximize regenerative potential.

Sphingosine kinase 1 improves cutaneous wound healing in diabetic rats

BACKGROUND

Diabetes is one of the most prevalent human metabolic diseases. Wound healing in diabetes is frequently impaired and treatment remains challenging. Sphingolipid metabolites play important roles in the regulation of glucose metabolism. SPK1 is the key enzyme in the sphingolipid metabolic pathway. S1P/SPK plays a pivotal role in the signalling pathways of diverse cellular processes including proliferation, differentiation, migration, apoptosis in diverse cell types.

METHODS

To investigate the role of sphingosine kinase 1 (SPK1) in skin injury, plasmids containing the SPK1 gene (pcDNA3-FLAG-SPK1) were applied to cutaneous wounds on a streptozotocin-induced diabetic rat model over a 21-day period. The wound area and rate of wound healing were determined. The histopathological features of the healed wounds were also observed, and SPK1 expression in the skin was detected by immunohistochemistry.

RESULTS

There was a significant decrease in wound area in diabetic rats treated with 125 and 60μg/wound pcDNA3-FLAG-SPK1 (P<0.001-0.01). The mean sizes of the wounds were 0.67±0.15cm(2), 0.83±0.18cm(2), and 1.09±0.23cm(2) in both treated and diabetic control group at the 7th day post-treatment respectively. In addition, wound healing in diabetic rats of test group was accelerated. At the 7th day, the mean rates of healing were 73.2±5.7% and 66±7.3% in test group of 125 and 60μg/wound respectively, and 55.4±9.9% in diabetic control group (P<0.001-0.01). Histology revealed that tissue sections from the treated diabetic rats contained more granulation tissue and capillaries than that of the control rats. There was high SPK1 expression in the skin of the treated diabetic rats.

CONCLUSIONS

SPK1 gene therapy may represent a novel approach to cutaneous wound healing.

Amphiphilic degradable polymers for immobilization and sustained delivery of sphingosine 1-phosphate

Controlled delivery of the angiogenic factor sphingosine 1-phosphate (S1P) represents a promising strategy for promoting vascularization during tissue repair and regeneration. In this study, we developed an amphiphilic biodegradable polymer platform for the stable encapsulation and sustained release of S1P. Mimicking the interaction between amphiphilic S1P and its binding proteins, a series of polymers with hydrophilic poly(ethylene glycol) core and lipophilic flanking segments of polylactide and/or poly(alkylated lactide) with different alkyl chain lengths were synthesized. These polymers were electrospun into fibrous meshes, and loaded with S1P in generally high loading efficiencies (>90%). Sustained S1P release from these scaffolds could be tuned by adjusting the alkyl chain length, blockiness and lipophilic block length, achieving 35-55% and 45-80% accumulative releases in the first 8h and by 7 days, respectively. Furthermore, using endothelial cell tube formation assay and chicken chorioallantoic membrane assay, we showed that the different S1P loading doses and release kinetics translated into distinct pro-angiogenic outcomes. These results suggest that these amphiphilic polymers are effective delivery vehicles for S1P and may be explored as tissue engineering scaffolds where the delivery of lipophilic or amphiphilic bioactive factors is desired.

Sphingolipids and antimicrobial peptides: function and roles in atopic dermatitis

Inflammatory skin diseases such as atopic dermatitis (AD) and rosacea were complicated by barrier abrogation and deficiency in innate immunity. The first defender of epidermal innate immune response is the antimicrobial peptides (AMPs) that exhibit a broad-spectrum antimicrobial activity against multiple pathogens, including Gram-positive and Gram-negative bacteria, viruses, and fungi. The deficiency of these AMPs in the skin of AD fails to protect our body against virulent pathogen infections. In contrast to AD where there is a suppression of AMPs, rosacea is characterized by overexpression of cathelicidin antimicrobial peptide (CAMP), the products of which result in chronic epidermal inflammation. In this regard, AMP generation that is controlled by a key ceramide metabolite S1P-dependent mechanism could be considered as alternate therapeutic approaches to treat these skin disorders, i.e., Increased S1P levels strongly stimulated the CAMP expression which elevated the antimicrobial activity against multiple pathogens resulting the improved AD patient skin.

Ceramide signaling in mammalian epidermis

Ceramide, the backbone structure of all sphingolipids, as well as a minor component of cellular membranes, has a unique role in the skin, by forming the epidermal permeability barrier at the extracellular domains of the outermost layer of the skin, the stratum corneum, which is required for terrestrial mammalian survival. In contrast to the role of ceramide in forming the permeability barrier, the signaling roles of ceramide and its metabolites have not yet been recognized. Ceramide and/or its metabolites regulate proliferation, differentiation, and apoptosis in epidermal keratinocytes. Recent studies have further demonstrated that a ceramide metabolite, sphingosine-1-phosphate, modulates innate immune function. Ceramide has already been applied to therapeutic approaches for treatment of eczema associated with attenuated epidermal permeability barrier function. Pharmacological modulation of ceramide and its metabolites' signaling can also be applied to cutaneous disease prevention and therapy. The author here describes the signaling roles of ceramide and its metabolites in mammalian cells and tissues, including the epidermis. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Effective healing of diabetic skin wounds by using nonviral gene therapy based on minicircle vascular endothelial growth factor DNA and a cationic dendrimer

BACKGROUND

The development of an efficient method to improve the wound healing process is urgently required for diabetic patients suffering a threat of limb amputations. Various growth factors have been proposed for treatment; however, more research still has to be carried out to maintain their curative effect. In the present study, we describe a simple nonviral gene therapy method for improving wound healing.

METHODS

Minicircle plasmid DNA encoding vascular endothelial growth factor (VEGF) was combined with an arginine-grafted cationic dendrimer, PAM-RG4. The formed complexes were injected subcutaneously into the skin wounds of diabetic mice.

RESULTS

Actively proliferating cells in wound tissue were efficiently transfected, resulting in a high level of VEGF expression. Within 6 days after injection, skin wounds in the diabetic mice were generally healed and displayed a well-ordered dermal structure, which was confirmed by histological staining.

CONCLUSIONS

This simple and effective gene therapy method may represent a powerful tool for the treatment of diabetic foot ulcers and other diseases that are refractory to treatment.

Vasculogenic cytokines in wound healing

Chronic wounds represent a growing healthcare burden that particularly afflicts aged, diabetic, vasculopathic, and obese patients. Studies have shown that nonhealing wounds are characterized by dysregulated cytokine networks that impair blood vessel formation. Two distinct forms of neovascularization have been described: vasculogenesis (driven by bone-marrow-derived circulating endothelial progenitor cells) and angiogenesis (local endothelial cell sprouting from existing vasculature). Researchers have traditionally focused on angiogenesis but defects in vasculogenesis are increasingly recognized to impact diseases including wound healing. A more comprehensive understanding of vasculogenic cytokine networks may facilitate the development of novel strategies to treat recalcitrant wounds. Further, the clinical success of endothelial progenitor cell-based therapies will depend not only on the delivery of the cells themselves but also on the appropriate cytokine milieu to promote tissue regeneration. This paper will highlight major cytokines involved in vasculogenesis within the context of cutaneous wound healing.

Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 2: role of growth factors in normal and pathological wound healing: therapeutic potential and methods of delivery

This is the second of 2 articles that discuss the biology and pathophysiology of wound healing, reviewing the role that growth factors play in this process and describing the current methods for growth factor delivery into the wound bed.

Engineering vascularized tissues using natural and synthetic small molecules

Vascular growth and remodeling are complex processes that depend on the proper spatial and temporal regulation of many different signaling molecules to form functional vascular networks. The ability to understand and regulate these signals is an important clinical need with the potential to treat a wide variety of disease pathologies. Current approaches have focused largely on the delivery of proteins to promote neovascularization of ischemic tissues, most notably VEGF and FGF. Although great progress has been made in this area, results from clinical trials are disappointing and safer and more effective approaches are required. To this end, biological agents used for therapeutic neovascularization must be explored beyond the current well-investigated classes. This review focuses on potential pathways for novel drug discovery, utilizing small molecule approaches to induce and enhance neovascularization. Specifically, four classes of new and existing molecules are discussed, including transcriptional activators, receptor selective agonists and antagonists, natural product-derived small molecules, and novel synthetic small molecules.

Role of S-1-P receptors and human vascular smooth muscle cell migration in diabetes and metabolic syndrome

BACKGROUND

Sphingosine-1-phosphate (S-1-P) is a bioactive sphingolipid released from activated platelets that stimulates migration of vascular smooth muscle cells (VSMC) in vitro. S-1-P is associated with oxidized low-density lipoprotein (oxLDL) and is important in vessel remodeling. S-1-P will activate multiple G protein-coupled receptors (S-1-PR 1 to 5), which can regulate multiple cellular functions, including cell migration. The aim of this study is to examine the role of S-1-PR signaling during smooth muscle cell migration in response to S-1-P.

METHODS

Human VSMCs were cultured in vitro. Expression of S-1-PR 1 to 5 was determined in conditions mirroring diabetes (40 mM glucose) and metabolic syndrome (25 mM glucose with 20 μM linoleic acid and 20 μM oleic acid). Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of S-1-P with and without siRNA against S-1-PR 1 to 5. Assays were performed for activation of ERK1/2, p38(MAPK) and JNK.

RESULTS

Human VSMCs express S-1-PR1, S-1-PR2, and S-1-PR3. There was no significant expression of S-1-PR4 and S-1-PR5. The expression of S-1-PR1 and S-1-PR3 is enhanced under high glucose conditions and metabolic syndrome conditions. Migration of VSMC in response to S-1-P is enhanced 2-fold by diabetes and 4-fold by metabolic syndrome. In diabetes, S-1-PR1 expression is enhanced, while S-1-PR2 and S-1-PR3 expression are both maintained. In metabolic syndrome, S-1-PR1 and 3 expressions are enhanced and that of S-1-PR2 is reduced. siRNA to S-1-PR1 results in a 2-fold reduction in S-1-P-mediated cell migration under all conditions. siRNA to S-1-PR2 enhanced cell migration only under normal conditions, while siRNA S-1-PR3 decreased migration in metabolic syndrome only. Down-regulation of S-1-PR1 reduced ERK1/2 activation in response to S-1-P, while that of S-1-PR2 had no effect under normal conditions. In diabetes, down-regulation of S-1-PR1 reduced activation of all three MAPKs. In metabolic syndrome, down-regulation of S-1-PR1 and S-1-PR3 reduced activation of all three MAPKs.

CONCLUSION

S-1-PR 1, 2, and 3 regulate human VSMC migration and their expression level and function are modulated by conditions simulating diabetes and metabolic syndrome.

S1P2 receptor mediates sphingosine-1-phosphate-induced fibronectin expression via MAPK signaling pathway in mesangial cells under high glucose condition

Accumulation of extracellular matrix including fibronectin in mesangium is one of the major pathologic characteristics in diabetic nephropathy. In the current study, we explored role of sphingosine-1-phosphate (S1P) receptor in fibronectin expression and underlying molecular mechanism. Among five S1P receptors the mRNA level of S1P2 receptor was the most abundant in kidney of diabetic rats and mesangial cells under high glucose condition. S1P augmentation of fibronectin was significantly inhibited by S1P2 receptor antagonist JTE-013 and S1P2-siRNA. S1P-stimulated fibronectin expression was remarkably blocked by ERK1/2 inhibitor PD98059 and p38MAPK inhibitor SB203580. Phospho-ERK1/2 and phospho-p38MAPK level induced by S1P were markedly abrogated by JTE-013 and S1P2-siRNA. In conclusion, S1P2 receptor was significantly up-regulated under diabetic condition. S1P2 receptor mediated fibronectin expression through the activation of S1P-S1P2-MAPK (ERK1/2 and p38MAPK) axis in mesangial cells under high glucose condition, suggesting that it might be a potential therapeutic target for diabetic nephropathy treatment.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.

Analysis of ceramide metabolites in differentiating epidermal keratinocytes treated with calcium or vitamin C

Ceramides (Cer) comprise the major constituent of sphingolipids in the epidermis and are known to play diverse roles in the outermost layers of the skin including water retention and provision of a physical barrier. In addition, they can be hydrolyzed into free sphingoid bases such as C₁₈ sphingosine (SO) and C₁₈ sphinganine (SA) or can be further metabolized to C₁₈ So-1-phosphate (S1P) and C₁₈ Sa-1-phosphate (Sa1P) in keratinocytes. The significance of ceramide metabolites emerged from studies reporting altered levels of SO and SA in skin disorders and the role of S1P and Sa1P as signaling lipids. However, the overall metabolism of sphingoid bases and their phosphates during keratinocyte differentiation remains not fully understood. Therefore, in this study, we analyzed these Cer metabolites in the process of keratinocyte differentiation. Three distinct keratinocyte differentiation stages were prepared using 0.07 mM calcium (Ca²⁺) (proliferation stage), 1.2 mM Ca²⁺ (early differentiation stage) in serum-free medium, or serum-containing medium with vitamin C (50 µL/mL) (late differentiation stage). Serum-containing medium was also used to determine whether vitamin C increases the concentrations of sphingoid bases and their phosphates. The production of sphingoid bases and their phosphates after hydrolysis by alkaline phosphatase was determined using high-performance liquid chromatography. Compared to cells treated with 0.07 mM Ca²⁺, levels of SO, SA, S1P, and SA1P were not altered after treatment with 1.2 mM Ca²⁺. However, in keratinocytes cultured in serum-containing medium with vitamin C, levels of SO, SA, S1P, and SA1P were dramatically higher than those in 0.07- and 1.2-mM Ca²⁺-treated cells; however, compared to serum-containing medium alone, vitamin C did not significantly enhance their production. Taken together, we demonstrate that late differentiation induced by vitamin C and serum was accompanied by dramatic increases in the concentration of sphingoid bases and their phosphates, although vitamin C alone had no effect on their production.

Sphingosine-1-phosphate induced vasoconstriction is increased in the isolated perfused kidneys of diabetic rats

We observed that in isolated perfused rat kidneys, sphingosine-1-phosphate produces S1P(2) receptor-mediated vasoconstriction, and this response increased in kidneys of diabetic rats. These results suggest that the antagonists of S1P(2) receptor may have potential as drugs to control diabetes-induced vascular complications.

The effect of dextrin-rhEGF on the healing of full-thickness, excisional wounds in the (db/db) diabetic mouse

Chronic wounds, such as ulceration of the lower limb, represent a significant clinical challenge in today's ageing society. With the aim of identifying improved therapeutics, we have previously described a bioresponsive, dextrin-recombinant human epidermal growth factor conjugate (dextrin-rhEGF), that (i) protects rhEGF against proteolytic degradation by human chronic wound fluid; and (ii) mediates rhEGF release by α-amylase, capable of stimulating increased proliferation/migration in normal dermal and chronic wound fibroblasts; and keratinocytes, in vitro. The aim of this study was to extend these findings, by investigating the effects of dextrin-rhEGF on wound healing in the (db/db) diabetic mouse, a widely used in vivo model of delayed wound healing. Standardised, full-thickness excisional wounds, created in the dorsal flank skin, were treated topically with succinoylated dextrin (50 μg/mL), rhEGF (10 μg/mL) or dextrin-rhEGF (1 or 10 μg/mL). Treatments were applied immediately after injury and subsequently on post-wounding, days 3 and 8. Wound healing was assessed macroscopically, in terms of initiation of neo-dermal tissue deposition and wound closure (including wound contraction and re-epithelialisation), over a 16 day period. Wound healing was assessed histologically, in terms of granulation tissue formation/maturity; cranio-caudal wound contraction and wound angiogenesis (CD31 immuno-staining), using tissues harvested at day 16. Blood samples were also analysed for α-amylase and rhEGF concentrations. In this established impaired wound healing model, the topically-applied dextrin-rhEGF significantly accelerated wound closure and neo-dermal tissue formation at the macroscopic level; and significantly increased granulation tissue deposition and angiogenesis at the histological level (p<0.05), relative to untreated, succinoylated dextrin and rhEGF alone controls. Overall, these findings support the further development of bioresponsive polymer conjugates, for tissue repair.

Selective activation of sphingosine 1-phosphate receptors 1 and 3 promotes local microvascular network growth

Proper spatial and temporal regulation of microvascular remodeling is critical to the formation of functional vascular networks, spanning the various arterial, venous, capillary, and collateral vessel systems. Recently, our group has demonstrated that sustained release of sphingosine 1-phosphate (S1P) from biodegradable polymers promotes microvascular network growth and arteriolar expansion. In this study, we employed S1P receptor-specific compounds to activate and antagonize different combinations of S1P receptors to elucidate those receptors most critical for promotion of pharmacologically induced microvascular network growth. We show that S1P(1) and S1P(3) receptors act synergistically to enhance functional network formation via increased functional length density, arteriolar diameter expansion, and increased vascular branching in the dorsal skinfold window chamber model. FTY720, a potent activator of S1P(1) and S1P(3), promoted a 107% and 153% increase in length density 3 and 7 days after implantation, respectively. It also increased arteriolar diameters by 60% and 85% 3 and 7 days after implantation. FTY720-stimulated branching in venules significantly more than unloaded poly(D, L-lactic-co-glycolic acid). When implanted on the mouse spinotrapezius muscle, FTY720 stimulated an arteriogenic response characterized by increased tortuosity and collateralization of branching microvascular networks. Our results demonstrate the effectiveness of S1P(1) and S1P(3) receptor-selective agonists (such as FTY720) in promoting microvascular growth for tissue engineering applications.

Sequential delivery of basic fibroblast growth factor and platelet-derived growth factor for angiogenesis

An externally regulated delivery model that permits temporal separation of multiple angiogenic factors was used for the delivery of basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF). While bFGF plays a significant role in the sprouting of new capillaries, PDGF plays a role in the recruitment of mural cells, which stabilize neovessels. However, these two factors have been shown to inhibit each other, when presented together. Using the externally regulated model, sequential delivery of bFGF and PDGF led to not only increased endothelial cell migration, but also endothelial cell and vascular pericyte colocalization. More importantly, this delivery strategy was able to induce red blood cell-filled neovessels, suggesting integration of angiogenesis with the existing vasculature.

Sequential delivery of vascular endothelial growth factor and sphingosine 1-phosphate for angiogenesis

Angiogenesis is an organized series of events, beginning with vessel destabilization, followed by endothelial cell re-organization, and ending with vessel maturation. Vascular endothelial growth factor (VEGF) aids in vascular permeability and endothelial cell recruitment while sphingosine 1-phosphate (S1P) stimulates vascular stability. Accordingly, VEGF may inhibit vessel stabilization while S1P may inhibit endothelial cell recruitment. For this reason, we created a new externally-regulated delivery model that not only permits sustained release of bioactive factors, but also temporal separation of the delivery of growth factors. Using this model, sequential delivery of factors was first confirmed in vitro with associated endothelial cells responding in a dose dependent manner. Furthermore, using a modified murine Matrigel plug model, it is apparent that delivery strategies where VEGF presentation is temporally separated from S1P presentation not only led to greater recruitment of endothelial cells, but also higher maturation index of associated vessels.

S1P metabolism in cancer and other pathological conditions

Nearly two decades ago, the sphingolipid metabolite sphingosine 1-phosphate was discovered to function as a lipid mediator and regulator of cell proliferation. Since that time, sphingosine 1-phosphate has been shown to mediate a diverse array of fundamental biological processes including cell proliferation, migration, invasion, angiogenesis, vascular maturation and lymphocyte trafficking. Sphingosine 1-phosphate acts primarily via signaling through five ubiquitously expressed G protein-coupled receptors. Intracellular sphingosine 1-phosphate molecules are transported extracellularly and gain access to cognate receptors for autocrine and paracrine signaling and for signaling at distant sites reached through blood and lymphatic circulation systems. Intracellular pools of sphingosine 1-phosphate available for signaling are tightly regulated primarily by three enzymes: sphinosine kinase, S1P lyase and S1P phosphatase. Alterations in sphingosine 1-phosphate as well as the enzymes involved in its synthesis and catabolism have been observed in many types of malignancy. These enzymes are being evaluated for their role in mediating cancer formation and progression, as well as their potential to serve as targets of anti-cancer therapeutics. In this review, the impact of sphingosine 1-phosphate, its cognate receptors, and the enzymes of sphingosine 1-phosphate metabolism on cell survival, apoptosis, autophagy, cellular transformation, invasion, angiogenesis and hypoxia in relation to cancer biology and treatment are discussed.

Therapeutic strategies for diabetes and complications: a role for sphingolipids?

Diabetes is a debilitating chronic disease that has no cure and can only be managed by pharmaceutical or nutritional interventions. Worldwide, the incidence of diabetes and diabetic complications is dramatically increasing. This may reflect the incomplete knowledge base underlying the role of inflammatory or nutritional stresses to exacerbate diabetic complications. Despite the knowledge that hyperlipidemia is a cardinal feature of both Type 1 and 2 diabetes, the actual lipid species that contribute to complications such as diabetic nephropathy, retinopathy, neuropathy and cardiovascular disease have not been well defined, or have not elucidated new treatment strategies. Sphingolipids comprise only a fraction of total lipids but a body of evidence has now identified dysfunctional sphingolipid metabolism and/or generation of specific sphingolipid metabolites as contributors to diabetic complications. This review suggests that pharmacological therapies that target dysfunctional sphingolipid metabolism and/or signaling may prove beneficial in decreasing the chronic pathology of hyperglycemia and hyperlipidemia. Moreover, the review suggests that these treatment options may also prove beneficial to ameliorate or delay pancreatic beta cell failure.

Mammalian Diaphanous (mDia) may be involved in the signal transduction of sphingosine-1-phosphate on developing actin stress fiber of human fibroblasts

Sphingosine 1-phosphate (S1P) is a biologically active lipid mediator with many pivotal roles in the regulation of cell growth, migration, differentiation, and apoptosis. However, signal transduction mediated by S1P in human fibroblasts is still unclear. We investigated signal transduction by S1P in human fibroblasts using collagen matrix contraction in order to explore whether or not S1P could be applied for the treatment of skin wound healing. We found that S1P promoted floating collagen matrices' contraction, for the in vitro model of initial phase wound contraction, in which some kinds of G protein, such as Gialpha, Rac 1, and Rho, were involved. However, Rho-associated coiled-coil forming kinase (ROCK) was partially involved in S1P-promoting floating collagen matrices contraction. Mammalian Diaphanous (mDia) as well as ROCK have been identified to be putative downstream target molecules of Rho. In mDia-silenced cells, the ROCK inhibitor suppressed actin stress fiber formation regardless of the presence or absence of S1P. Our results indicate that mDia as well as ROCK may be situated downstream of Gialpha, Rac1, and Rho to induce actin stress fiber development by human fibroblasts stimulated with SIP.

Normalization of diabetic wound healing

HYPOTHESIS

Impaired wound healing in diabetics is due to pathologic angiogenesis, which is a result of aberrant sphingosine-1-phosphate signaling. Pharmacologic modulation of sphingosine-1-phosphate-dependent signaling normalizes healing in diabetic wounds.

Lyase to live by: sphingosine phosphate lyase as a therapeutic target

BACKGROUND

Sphingosine 1-phosphate (S1P) is a bioactive lipid that regulates cell proliferation, survival and migration and plays an essential role in angiogenesis and lymphocyte trafficking. S1P levels in the circulation and tissues are tightly regulated for proper cell functioning, and dysregulation of this system may contribute to the pathophysiology of certain human diseases. Sphingosine phosphate lyase (SPL) irreversibly degrades S1P and thereby acts as a gatekeeper that regulates S1P signaling by modulating intracellular S1P levels and the chemical S1P gradient that exists between lymphoid organs and circulating blood and lymph. However, SPL also generates biochemical products that may be relevant in human disease. SPL has been directly implicated in various physiological and pathological processes, including cell stress responses, cancer, immunity, hematopoietic function, muscle homeostasis, inflammation and development.

OBJECTIVE/METHODS

This review summarizes the current know-ledge of SPL structure, function and regulation, its involvement in various disease states and currently available small molecules known to modulate SPL activity.

RESULTS/CONCLUSION

This review provides evidence that SPL is a potential target for pharmacological manipulation for the treatment of malignant, autoimmune, inflammatory and other diseases.

The effect of topical extract of Momordica charantia (bitter gourd) on wound healing in nondiabetic rats and in rats with diabetes induced by streptozotocin

BACKGROUND

Momordica charantia (MC; bitter gourd) is a traditional herb commonly used for its antidiabetic, antioxidant, contraceptive and antibacterial properties. It is also used for the rapid healing of wounds.

AIM

To observe the topical effect of MC extract on the wound-healing process in rats with diabetes induced by streptozotocin.

METHODS

In total, 72 Sprague-Dawley rats were used for the study. The animals were subdivided into two groups: a nondiabetic group (n = 36) and a group with diabetes induced by streptozotocin (n = 36). Both groups were subdivided further into a nontreated control group (n = 18), and a topically treated group with MC extract administered daily (n = 18). The wound was inflicted with a 6-mm punch-biopsy needle on the dorsal aspect of the thoracolumbar region. The animals were killed on the days 1, 5 and 10 after wound creation. The rate of wound closure and the total protein content was estimated. Histological study of the wound tissue at days 5 and 10 was also performed.

RESULTS

The diabetic group exhibited delayed wound healing as compared to the normal group. Interestingly, the diabetic group treated with topical MC extract showed better results than the nontreated group.

CONCLUSION

Results show that administration of MC extract improves and accelerates the process of wound healing in diabetic animals.

Models for diabetic wound healing and healing into percutaneous devices

Delayed healing of chronic ulcers in patients with diabetes and infections resulting from percutaneous medical devices (e.g., vascular access catheters) not only plays a major role in morbidity and mortality, but is a major burden to our healthcare system. In this paper, we review models to study diabetic wound healing and the wound-healing response associated with implanted percutaneous implants.

"Inside-out" signaling of sphingosine-1-phosphate: therapeutic targets

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite involved in many critical cellular processes including proliferation, survival, and migration, as well as angiogenesis and allergic responses. S1P levels inside cells are tightly regulated by the balance between its synthesis by sphingosine kinases and degradation. S1P is interconvertible with ceramide, which is a critical mediator of apoptosis. It has been postulated that the ratio between S1P and ceramide determines cell fate. Activation of sphingosine kinase by a variety of agonists increases intracellular S1P, which in turn can function intracellularly as a second messenger or be secreted out of the cell and act extracellularly by binding to and signaling through S1P receptors in autocrine and/or paracrine manners. Recent studies suggest that this "inside-out" signaling by S1P may play a role in many human diseases, including cancer, atherosclerosis, inflammation, and autoimmune disorders such as multiple sclerosis. In this review we summarize metabolism of S1P, mechanisms of sphingosine kinase activation, and S1P receptors and their downstream signaling pathways and examine relationships to multiple disease processes. In particular, we describe recent preclinical and clinical trials of therapies targeting S1P signaling, including 2-amino-2-propane-1,3-diol hydrochloride (FTY720, fingolimod), S1P receptor agonists, sphingosine kinase inhibitors, and anti-S1P monoclonal antibody.

Sphingosine 1-phosphate attenuates H2O2-induced apoptosis in endothelial cells

Reactive oxygen species including H(2)O(2) lead vascular endothelial cells (EC) to undergo apoptosis. Sphingosine 1-phosphate (S1P) is a platelet-derived sphingolipid mediator that elicits various EC responses. We aimed to explore whether and how S1P modulates EC apoptosis induced by H(2)O(2). Treatment of cultured bovine aortic EC (BAEC) with H(2)O(2) (750 microM for 6h) led to DNA fragmentation (ELISA), DNA nick formation (TUNEL staining), and cleavage of caspase-3, key features of EC apoptosis. These responses elicited by H(2)O(2) were alike markedly attenuated by pretreatment with S1P (1 microM, 30 min). H(2)O(2) induced robust phosphorylation of both p38 and JNK MAP kinases. However, pretreatment with S1P decreased phosphorylation of only p38 MAP kinase, but not that of JNK; conversely, an inhibitor of p38 MAP kinase, but not that of JNK, attenuated H(2)O(2)-induced caspase-3 activation. Thus S1P attenuates H(2)O(2)-induced apoptosis of cultured BAEC, involving p38 MAP kinase.