Peptide hormone relaxin: from bench to bedside.

Although pioneering preclinical research on the use of cell therapy for cardiac regeneration was conducted in the last quarter of the 20th century,1,2 a preponderance of advances have occurred in the 21st century, making this a relatively young field. In the first important clinical trial of cardiac cell therapy, begun in 2001, Menasche et al3 implanted autologous skeletal myoblasts into postinfarct scar at the time of coronary artery bypass surgery. Although the transplanted cells remained viable and exhibited contraction, they formed the nidus for serious ventricular tachyarrhythmias, which led to premature discontinuation of the trial. Despite this outcome, the trial energized the field, accelerating both preclinical and clinical research, albeit not with skeletal myoblasts. The extensive progress in cardiac regeneration is reviewed in this Compendium, and as occurs frequently in science, important observations have led to more questions and challenges (Table). View this table: Table. Important Challenges to Cell Therapy for Cardiac Regeneration Many cell types have been evaluated as candidates for cardiac regeneration. Among the earliest clinical trials, Zeiher’s group infused autologous bone marrow-derived progenitor cells into the coronary arteries of patients with acute,4 as well as healed myocardial infarction (MI)5 and reported improvements in left ventricular (LV) function. However, these results have not been fully confirmed by later studies, as pointed out in the review in the Compendium by Banarjee, Bolli, and Hare.6 Pittenger et al7 were among the first to direct attention to bone marrow-derived (stromal) mesenchymal stem cells (MSCs), emphasizing that these cells proliferated extensively in culture and suggesting that they could be attractive candidates for transplantation. In 2004, Chen et al8 reported that intracoronary infusion of autologous bone marrow-derived MSCs improved cardiac function. Zimmet and Hare pointed out that MSCs lack histocompatibility type II markers and elude rejection by …

T he cardiovascular disease (CVD) risk associated with diabetes mellitus (DM) has become increasingly evident, accounting for Ϸ80% of deaths among patients with this disease 1 and making CVD risk modification a key therapeutic objective in diabetic patients.2][3][4] The rapidly increasing global burden of DM, 5 coupled with the associated CVD risk, underscores the imperative for continued generation and application of evidence-based therapies to reduce CVD risk in this high-risk cohort.In this 2-part series, we first review the CVD effects of the thiazolidinedione medications, the most broadly investigated class of antihyperglycemic drugs evaluated in the context of CVD risk.In the second part, we review the modulators of the incretin axis that have most recently achieved US Food and Drug Administration approval, with a focus on CVD considerations; introduce selected drugs in advanced development; summarize glucose control strategies for cardiovascular patients; and discuss the regulatory review of glucose-lowering medications.

[EMBARGOED UNTIL 6/1/2023] Objective: Heart failure with preserved ejection fraction (HFpEF) is a disease associated with significant clinical pathophysiological heterogeneity in which maladaptive cardiac fibrosis, in both the right and left ventricles of the heart, plays a unique role in the manifestation of disease. Fibrotic remodeling quantified in this project occurs in a chamber-dependent manner on both sides of the heart. Extracellular matrix (ECM) remodeling is the core of this pathological process. The prevalence of HFpEF is greater in postmenopausal women with hypertension. Therefore, the goal of this study was to assess the role of female sex hormones on chamber-dependent differences i.e., left ventricle (LV) vs. right ventricle (RV), in ECM remodeling and regulation in a mini-swine model of pressure overload-induced heart failure (HF). To gain insight about the regulation of fibrosis in this model, biological inputs were measured in both the right and left ventricles and used as input variables in an artificial neural network model (ANN). This model will identify best predictors for experimental group status i.e., the combination of the loss of female sex hormone and/or pressure overload status, as an indication for the biological roles they play in the fibrotic remodeling process. Hypothesis: I hypothesized molecular markers involved in the bioregulation of the cardiac ECM can predict experimental group status in a chamber-specific manner. Methods: a) Animal model: An ovariectomy (OVX) model of surgically induced menopause was used to model the loss of female sex hormones. Separately, aortic banding (AB) was used to induce pressure-overload and mimic HFpEF. Animals that did not undergo ovariectomy were assigned to the intact (INT) groups and animals that did not undergo AB were assigned as control (CON). b) Data: 24 six month old female swine were categorized into 4 groups by ovariectomy and aortic-banded status: 1) Control, intact (CON-INT; n=6); 2) CON-OVX (n=5); 3) AB-INT (n=7) ;and 4) AB-OVX (n=6). c) Ninety-six biological measurements from both the LV and RV were considered including different mRNA, proteins, activity and/or abundance levels of various extracellular matrix components including structural proteins and regulatory pathways. d) Data preprocessing: Missing data were mean imputed and the min-max normalization method was used for all measures. One-way ANOVA models were used to identify mRNA or protein targets associated with group status for consideration in the ANN. Data were split into testing and training sets with one observation from each group (n=4 total) retained for later model testing i.e., 84 percent training and 16 percent testing e) Artificial neural network model: Measurements associated with group status were then used as input features in the ANN model. Multiple activation functions were considered. Different combinations of hidden layers and nodes within each layer were optimized. Cross-validation, confusion matrices, and F1 scores, percentage accuracy and balanced accuracy for each experimental group were used to describe the accuracy of the developed ANN model. Results: One-way ANOVA models indicated that in the LV, total collagen content, TIMP-1 mRNA, total JNK protein level, MMP-14 activity, MMP-2 activity and collagen I mRNA were associated with group status (p [less than] 0.1). In the RV, total collagen content and collagen I and III mRNA levels were associated with group status (p [less than] 0.1). These nine molecular markers were used to develop the ANN model. Cross-validation and confusion matrices indicate all nine targets formed a linear relationship predictive of group with an overall accuracy of 70.7 percent and F1 score of 0.81. Conclusion: Molecular mechanisms involved in the bioregulation of the ECM have analytical power to determine sex hormone and aortic-banding status in a pre-clinical model of pressure overload-induced HF. These findings indicate that nine biological measures could predict experimental group status in our pre-clinical swine model. Therefore, I identified these variables as potential biomarkers of fibrotic remodeling in a HFpEF phenotype with loss of female sex hormones and pressure overload. I also highlight the importance of these nine variables in the fibrotic remodeling process on both sides of the heart.

Over 15 years after hepatotoxicity was first observed following administration of an adeno-associated virus (AAV) vector during a hemophilia B clinical trial, recent reports of treatment-associated neurotoxicity in animals and humans have brought the potential impact of AAV-associated toxicity back to prominence. In both pre-clinical studies and clinical trials, systemic AAV administration has been associated with neurotoxicity in peripheral nerve ganglia and spinal cord. Neurological signs have also been seen following direct AAV injection into the brain, both in non-human primates and in a clinical trial for late infantile Batten disease. Neurotoxic events appear variable across species, and preclinical animal studies do not fully predict clinical observations. Accumulating data suggest that AAV-associated neurotoxicity may be underdiagnosed and may differ between species in terms of frequency and/or severity. In this review, we discuss the different animal models that have been used to demonstrate AAV-associated neurotoxicity, its potential causes and consequences, and potential approaches to blunt AAV-associated neurotoxicity.

The recently emerged Zika virus (ZIKV) spread to the Americas, causing a spectrum of congenital diseases including microcephaly in newborn and Guillain-Barré syndrome (GBS) in adults. The unprecedented nature of the epidemic and serious diseases associated with the viral infections prompted the global research community to understand the immunopathogenic mechanisms of the virus and rapidly develop safe and efficacious vaccines. This has led to a number of ZIKV vaccine candidates that have shown significant promise in human clinical trials. These candidates include nucleic acid vaccines, inactivated vaccines, viral-vectored vaccines, and attenuated vaccines. Additionally, a number of vaccine candidates have been shown to protect animals in preclinical studies. However, as the epidemic has waned in the last three years, further development of the most promising vaccine candidates faces challenges in clinical efficacy trials, which is needed before a vaccine is brought to licensure. It is important that a coalition of government funding agencies and private sector companies is established to move forward with a safe and effective vaccine ready for deployment when the next ZIKV epidemic occurs.

Heart failure is a major co-morbid association of diabetes mellitus. The incidence of heart failure in diabetic vs. control subjects is 2- to 3-fold greater in every decade of life.1 Similar data on prevalence have also been observed in the Framingham study.2 Conversely, diabetes represents a major co-morbidity in patients with heart failure. In both clinical trials and registries of heart failure patients, between 24% and 44% have known diabetes mellitus.3 A key epidemiological issue in the context of discussion of therapies for diabetes and the associated risk of heart failure is the impact of glycaemic control on heart failure risk. Both UKPDS4 and a large cohort investigated by Iribarren et al.5 have demonstrated a close positive linear relationship between haemoglobin A1c levels and rate of heart failure development. Specifically, poorest glycaemic control was associated with greatest risk of heart failure. However, studies such as UKPDS demonstrated that more intensive glycaemic control was not associated with reduced development of heart failure.6 More contemporaneous meta-analyses have supported this observation,7 albeit potentially driven by drug treatments such as thiazolidinediones which may contribute to heart failure development. Based on pre-clinical and early clinical work, dipeptidyl peptidase-4 (DPP-4) inhibitors should, in theory, have beneficial rather than adverse effects on progression of LV remodelling and therefore delay development of symptomatic heart failure8 (Figure 1). Dipeptidyl peptidase-4 is involved in the enzymatic breakdown of glucagon-like peptide (GLP)-1; thus, DPP-4 inhibition augments circulating GLP-1 levels, which appears to have beneficial effects upon the heart in animal models as well as in the post-myocardial infarction and established heart failure settings in man.9 DPP-4 stimulates activation of proinflammatory cytokines,9 independent drivers of progression of LV systolic dysfunction due to their prohypertrophic and profibrotic effects.10 Inhibition of DPP-4 augments circulating levels of soluble-derived factor (SDF)-1 α,9 a stimulant of bone marrow production of erythroid precursor cells, which should contribute to improved vascular and myocardial function. Finally, DPP-4 inhibition should direct BNP metabolism towards an increase in active BNP rather than biologically inactive BNP precursor fragments.9 Pre-clinical studies with DPP-4 inhibitors in animal models of LV systolic dysfunction11 support a beneficial effect on LV remodelling and survival in comparison with controls. Published and ongoing major cardiovascular outcome trials with DPP-4 inhibitors are summarized in Table 1. Three major DPP-4 inhibitor trials have recently reported, all with implications for heart failure, and these are examined in greater detail below. The SAVOR-TIMI 53 trial compared the DPP-4 inhibitor, saxagliptin, with placebo in the setting of patients with a history of, or who are at risk of, cardiovascular events.12 There was no overall effect of saxagliptin vs. placebo on the primary endpoint of time to first event of cardiovascular death, myocardial infarction, or ischaemic stroke. However, patients in the saxagliptin group were more likely to be hospitalized for heart failure than those in the placebo group [3.5 vs. 2.8%, hazard ratio (HR) 1.27, 95% confidence interval (CI) 1.07–1.51, P = 0.007]. A Kaplan–Meier plot of accrual of heart failure hospitalizations over time showed an early divergence of the curves which continued to diverge slightly beyond the first 180 days of treatment.13 A Forrest plot of key baseline variables that may influence risk of heart failure hospitalization according to treatment did not demonstrate any heterogeneity, with all pre-defined subgroups trending towards an excess of primary endpoint events with saxagliptin vs. placebo. One exception may be baseline plasma NT-proBNP levels. In those patients within the highest BNP quartile (333–46627 pg/mL), 10.9% of saxagliptin and 8.9% of placebo patients had a hospitalization for heart failure (P = 0.024). The EXAMINE study assessed the DPP-4 inhibitor, alogliptin, in patients who had recently had an acute coronary syndrome.14 As with saxagliptin in SAVOR, there was no significant effect of this class on the primary endpoint (death from cardiovascular causes, non-fatal myocardial infarction, or non-fatal stroke). In EXAMINE, 3.9% of alogliptin-treated and 3.3% of placebo-treated patients had a hospitalization for heart failure (HR 1.19, 95% CI 0.89–1.58, P = NS).15 This was a pre-defined exploratory endpoint that was independently adjudicated. In EXAMINE, 28% of patients had a history of congestive heart failure at baseline. The primary EXAMINE endpoint was reduced with alogliptin vs. placebo, HR 0.82, P = 0.2015, in these patients. Data on recurrent heart failure hospitalizations within this subgroup have not as yet been reported. The Vildagliptin In Ventricular Dysfunction Diabetes (VIVIDD) trial has been presented16 but not yet published. All patients in VIVIDD had evidence of symptomatic systolic heart failure with an LVEF <35% as well as diabetes requiring glucose-lowering therapy. There was no difference in adjudicated heart failure events between vildagliptin (n = 128, 18%) and placebo (n = 125, 17.6%) patients over the 52 weeks of the study. The primary endpoint of the VIVIDD study was change in LVEF, with no difference observed between treatment groups (+0.54, 95% CI –1.97 to 3.06, P = 0.67). Interestingly, plasma BNP levels were reduced in both groups: vildagliptin, ratio of 0.72 vs. baseline; placebo, 0.86 vs. baseline. Somewhat surprisingly, LV diastolic and systolic volumes were both increased with vildagliptin compared with placebo. Our group recently performed a meta-analysis of heart failure outcomes with DPP-4 inhibitors, including the above studies. Forest plots of these data, comparing DPP-4 inhibitor with placebo and an active comparator, are shown in Figure 2. A sensitivity analysis was also undertaken, with thiazolidenediones included and excluded as comparator. With thiazolidenediones included, the risk ratio for heart failure with DPP-4 inhibitors was 0.80, 95% CI 0.35–1.81, P = 0.59. With thiazolidenediones removed as comparator, the risk ratio for heart failure was 1.15, 95% CI 1.00–1.33, P = 0.04. It is not entirely certain whether DPP-4 inhibitors directly or even indirectly cause heart failure, but if one accepts the premise that this is the case, then a number of potential explanations need to be considered. It is entirely plausible that the increase in heart failure events observed, particularly in SAVOR,12 represents the play of chance. There is a long history of ‘play of chance’ influencing cardiovascular trials. This is particularly true of subgroup analysis, but would equally apply to analysis of ‘off-target’ effects of drugs.17 Nevertheless, there are hints with DPP-4 inhibitors that this may not be the case, especially given the numerical increase in events in EXAMINE14 and the odd remodelling effects of vildagliptin in VIVIDD.16 Furthermore, there was an excess (not significant) of all-cause mortality events with vildagliptin amongst patients in VIVIDD.24 Although SAVOR and EXAMINE were large trials and baseline characteristics appear to be well balanced, it is certainly possible that there were imbalances at baseline between groups, which may have led to an increase in risk of heart failure hospitalization with the DPP-4 inhibitor. Specifically, there may be imbalances in background medications that are known to retard heart failure progression, such as ACE inhibitors. It would certainly be prudent to look at the patients who did have a heart failure hospitalization to see if there are baseline imbalances within this specific subgroup. Hypoglycaemia stimulates the sympathetic and renin–angiotensin–aldosterone systems and, thus, with chronic stimulation, may have adverse consequences including progression to symptomatic heart failure. However, the increase in rates of hypoglycaemia in both SAVOR and EXAMINE were very modest compared with the placebo group. An increase in relative risk for hypoglycaemia with saxagliptin in SAVOR was noted in patients on background sulfonylureas.12 However, when this subgroup was examined, there was no increase in risk of heart failure hospitalization with saxagliptin.13 Similarly, in EXAMINE, differences in hypoglycaemia were very minor between the alogliptin and placebo groups.14 Marney et al.18 suggested that sitagliptin interacted with high-dose enalapril to increase rather than decrease blood pressure levels in metabolic syndrome patients. This was associated with an increase in heart rate and plasma norepinephrine levels that was significant at the highest dose of enalapril. The mechanisms underlying this interaction are unclear but may relate to blockade of the peptides substance P and/or neuropeptide Y with DPP-4 inhibitors, leading to sympathetically mediated vasoconstriction. Similarly, Jackson et al.19 demonstrated that, in a renal perfusion model, enhancement of angiotensin II-mediated constrictor responses due to increasing neuropeptide Y administration could be exacerbated by sitagliptin and blocked if sitagliptin is given with a neuropeptide Y inhibitor. If the above are correct, then attention to heart rate and blood pressure responses in the major DPP-4 outcome trials would be of considerable interest. However, an analysis of earlier, much smaller saxagliptin studies20 suggested that (either as monotherapy or in combination) there was little impact on blood pressure with the DPP-4 inhibitor in comparison with placebo or metformin. The recent major DPP-4 inhibitor outcome studies have raised the hypothesis that heart failure may be precipitated and/or exacerbated with the use of these agents in the management of patients with diabetes. This is surprising given that preceding DPP-4 inhibitor data suggested potential for theoretical benefit with regard to HF, on the basis of the mechanisms outlined above.8, 9 This may represent play of chance and/or imbalances across study groups, but, if real, mechanisms urgently need to be elucidated. Until more data are available, guideline recommendations should be followed, but undoubtedly greater vigilance should be applied to recognizing the development of clinically significant HF in DPP-4 inhibitor-treated patients, including careful clinical assessment of heart failure symptoms and signs, together with (as required) ancillary objective assessments of heart failure status including measurement of plasma BNP levels and echocardiography. Two large-scale, placebo-controlled outcome trials, TECOS (with sitagliptin) and CARMELINA (with linagliptin), are due to report in the next few years, which should provide important data to support or refute the above hypothesis. In the meantime, a mechanistic explanation for this potential link should be further explored. Conflict of interest: none declared.

Response to letter to the Editor – Implementation of integrative approaches to improve the design of Crohn's disease clinical trials

Infection by the intracellular bacterial pathogen Mycobacterium tuberculosis (Mtb) is a major cause of morbidity and mortality worldwide. Slow progress has been made in lessening the impact of tuberculosis (TB) on human health, especially in parts of the world where Mtb is endemic. Due to the complexity of TB disease, there is still an urgent need to improve diagnosis, prevention, and treatment strategies to control global spread of disease. Active research targeting avenues to prevent infection or transmission through vaccination, to diagnose asymptomatic carriers of Mtb, and to improve antimicrobial drug treatment responses is ongoing. However, this research is hampered by a relatively poor understanding of the pathogenesis of early infection and the factors that contribute to host susceptibility, protection, and the development of active disease. There is increasing interest in the development of adjunctive therapy that will aid the host in responding to Mtb infection appropriately thereby improving the effectiveness of current and future drug treatments. In this review, we summarize what is known about the host response to Mtb infection in humans and animal models and highlight potential therapeutic targets involved in TB granuloma formation and resolution. Strategies designed to shift the balance of TB granuloma formation toward protective rather than destructive processes are discussed based on our current knowledge. These therapeutic strategies are based on the assumption that granuloma formation, although thought to prevent the spread of the tubercle bacillus within and between individuals contributes to manifestations of active TB disease in human patients when left unchecked. This effect of granuloma formation favors the spread of infection and impairs antimicrobial drug treatment. By gaining a better understanding of the mechanisms by which Mtb infection contributes to irreversible tissue damage, down regulates protective immune responses, and delays tissue healing, new treatment strategies can be rationally designed. Granuloma-targeted therapy is advantageous because it allows for the repurpose of existing drugs used to treat other communicable and non-communicable diseases as adjunctive therapies combined with existing and future anti-TB drugs. Thus, the development of adjunctive, granuloma-targeted therapy, like other host-directed therapies, may benefit from the availability of approved drugs to aid in treatment and prevention of TB. In this review, we have attempted to summarize the results of published studies in the context of new innovative approaches to host-directed therapy that need to be more thoroughly explored in pre-clinical animal studies and in human clinical trials.

Adult-derived mesenchymal stem cells have received considerable attention over the past two decades for their potential use in tissue engineering, principally because of their potential to differentiate into multiple stromal-cell lineages. Recently, the immunomodulatory properties of mesenchymal stem cells have attracted interest as a unique property of these cells that may be harnessed for novel therapeutic approaches in immune-mediated diseases. Mesenchymal stem cells have been shown to inhibit the proliferation of activated T-cells both in vitro and in vivo but to stimulate T-regulatory cell proliferation. Mesenchymal stem cells are also known to be weakly immunogenic and to exert immunosuppressive effects on B-cells, natural killer cells, dendritic cells and neutrophils through various mechanisms. Furthermore, intravenous administration of allogeneic mesenchymal stem cells has shown a marked suppression of host immune reactions in preclinical animal models of large-organ transplant rejection and in various autoimmune- and inflammatory-based diseases. Some clinical trials utilizing human mesenchymal stem cells have also produced promising outcomes in patients with graft-vs.-host disease and autoimmune diseases. Mesenchymal stem cells identified from various dental tissues, including periodontal ligament stem cells, also possess multipotent and immunomodulatory properties. Hence, dental mesenchymal stem cells may represent an alternate cell source, not only for tissue regeneration but also as therapies for autoimmune- and inflammatory-mediated diseases. These findings have elicited interest in dental tissue mesenchymal stem cells as alternative cell sources for modulating alloreactivity during tissue regeneration following transplantation into human leukocyte antigen-mismatched donors. To examine this potential in periodontal regeneration, future work will need to assess the capacity of allogeneic periodontal ligament stem cells to regenerate periodontal ligament in animal models of periodontal disease. The present review describes the immunosuppressive effects of mesenchymal stem cells on various types of immune cells, the potential mechanisms through which they exert their mode of action and the preclinical animal studies and human clinical trials that have utilized mesenchymal stem cells, including those populations originating from dental structures.

While the duration and size of human clinical trials may be difficult to reduce, there are several parameters in pre-clinical vaccine development that may be possible to further optimise. By increasing the accuracy of the models used for pre-clinical vaccine testing, it should be possible to increase the probability that any particular vaccine candidate will be successful in human trials. In addition, an improved model will allow the collection of increasingly more-informative data in pre-clinical tests, thus aiding the rational design and formulation of candidates entered into clinical evaluation. An acceleration and increase in sophistication of pre-clinical vaccine development will thus require the advent of more physiologically-accurate models of the human immune system, coupled with substantial advances in the mechanistic understanding of vaccine efficacy, achieved by using this model. We believe the best viable option available is to use human cells and/or tissues in a functional in vitro model of human physiology. Not only will this more accurately model human diseases, it will also eliminate any ethical, moral and scientific issues involved with use of live humans and animals. An in vitro model, termed "MIMIC" (Modular IMmune In vitro Construct), was designed and developed to reflect the human immune system in a well-based format. The MIMIC System is a laboratory-based methodology that replicates the human immune system response. It is highly automated, and can be used to simulate a clinical trial for a diverse population, without putting human subjects at risk. The MIMIC System uses the circulating immune cells of individual donors to recapitulate each individual human immune response by maintaining the autonomy of the donor. Thus, an in vitro test system has been created that is functionally equivalent to the donor's own immune system and is designed to respond in a similar manner to the in vivo response.

<i>Circulation: Cardiovascular Interventions</i> Editors’ Picks

<i>Circulation</i> Editors’ Picks

BackgroundErythropoiesis stimulating agents (ESAs) were proposed to enhance survival of renal tissues through direct effects via activation of EPO receptors on renal cells resulting in reduced cell apoptosis, or indirect effects via increased oxygen delivery due to increased numbers of Hb containing red blood cells. Thus through several mechanisms there may be benefit of ESA administration on kidney disease progression and kidney function in renal patients. However conflicting ESA reno-protection outcomes have been reported in both pre-clinical animal studies and human clinical trials. To better understand the potential beneficial effects of ESAs on renal-patients, meta-analyses of clinical trials is needed.MethodsLiterature searches and manual searches of references lists from published studies were performed. Controlled trials that included ESA treatment on renal patients with relevant renal endpoints were selected.ResultsThirty two ESA controlled trials in 3 categories of intervention were identified. These included 7 trials with patients who had a high likelihood of AKI, 7 trials with kidney transplant patients and 18 anemia correction trials with chronic kidney disease (predialysis) patients. There was a trend toward improvement in renal outcomes in the ESA treated arm of AKI and transplant trials, but none reached statistical significance. In 12 of the anemia correction trials, meta-analyses showed no difference in renal outcomes with the anemia correction but both arms received some ESA treatment making it difficult to assess effects of ESA treatment alone. However, in 6 trials the low Hb arm received no ESAs and meta-analysis also showed no difference in renal outcomes, consistent with no benefit of ESA/ Hb increase.ConclusionsMost ESA trials were small with modest event rates. While trends tended to favor the ESA treatment arm, these meta-analyses showed no reduction of incidence of AKI, no reduction in DGF or improvement in 1-year graft survival after renal transplantation and no significant delay in progression of CKD. These results do not support significant clinical reno-protection by ESAs.

The development and maintenance of an adequate vascular supply is critical for the viability of normal and neoplastic tissues. Angiogenesis, the development of new blood vessels from preexisting capillary networks, plays an important role in a number of physiologic and pathologic processes, including reproduction, wound repair, inflammatory diseases, and tumor growth. Angiogenesis involves sequential steps that are triggered in response to angiogenic growth factors released by inflammatory, mesenchymal, or tumor cells that act as ligands for endothelial cell receptor tyrosine kinases. Stimulated endothelial cells detach from neighboring cells and migrate, proliferate, and form tubes. The immature tubes are subsequently invested and stabilized by pericytes or smooth muscle cells. Angiogenesis depends upon complex interactions among various classes of molecules, including adhesion molecules, proteases, structural proteins, cell surface receptors, and growth factors. The therapeutic manipulation of angiogenesis targeted against ischemic and neoplastic diseases has been investigated in preclinical animal models and in clinical trials. Proangiogenic trials that have stimulated vessel growth in ischemic coronary or peripheral tissues through expression, delivery, or stimulated release of growth factors have shown efficacy in animal models and mixed results in human clinical trials. Antiangiogenic trials have used strategies to block the function of molecules critical for new vessel growth or maturation in the treatment of a variety of malignancies, mostly with results less encouraging than those seen in preclinical models. Pro-and antiangiogenic clinical trials demonstrate that strategies for optimal drug delivery, dosing schedules, patient selection, and endpoint measurements need further investigation and refinement before the therapeutic manipulation of angiogenesis will realize its full clinical potential.

Tyrosinase (EC 1.14.18.1) is a pivotal enzyme that catalyzes the conversion of L-tyrosine to dopaquinone through a dual oxidation process, initiating melanin biosynthesis. Melanin plays a critical role in various biological processes, and its overproduction is associated with multiple conditions. Tyrosinase plays a crucial role in immune regulation by regulating the activity of immune cells and enhancing the immune response of the body. It is essential for maintaining skin health and preventing autoimmune diseases. In addition, tyrosinase has shown potential in immunotherapy, especially in the treatment of malignant melanoma and autoimmune diseases such as vitiligo. Inhibiting tyrosinase to reduce melanin synthesis has emerged as a promising therapeutic strategy with applications in skin whitening, melasma treatment, acne management, Parkinson's disease (PD) intervention, melanoma prevention, and overcoming immunotherapy resistance. By leveraging the tyrosinase-related comprehensive data documented in the BRENDA database, we have systematically summarized the effective information, including its classification, structural characteristics, catalytic functions, biosynthesis pathways, substrate specificity profiles, reaction products, and associated disease mechanisms, and so forth. This review comprehensively examines the therapeutic mechanisms, development history, and current clinical status of tyrosinase inhibitors at preclinical and advanced stages. We highlight recent research progress, focusing on evidence from animal models, preclinical studies, and human clinical trials across different indications. Additionally, we critically analyze the challenges and limitations in the field and provide insights into future directions for optimizing tyrosinase inhibitors. By synthesizing current knowledge and advancements, this review aims to underscore the therapeutic potential of tyrosinase inhibition and its role in addressing diverse medical needs.