Curcumin suppress inflammatory response in traumatic brain injury via p38/MAPK signaling pathway

Curcumin Treatment Ameliorates Hepatic Insulin Resistance Induced by Sub-chronic Oral Exposure to Cadmium LOAEL Dose via NF-κB and Nrf2 Pathways

Cadmium (Cd) is a global pollutant, and its accumulation in the liver causes oxidative stress, inflammation, insulin resistance (IR), and metabolic complications. This study investigated whether curcumin treatment could alleviate hepatic IR in Wistar rats exposed to sub-chronic cadmium and explored the underlying molecular pathways. Male Wistar rats were divided into a control group (standard normocaloric diet + cadmium-free water) and a cadmium group (standard normocaloric diet + drinking water with 32.5 ppm CdCl2) for 30 days. Oral glucose tolerance, insulin response, and IR were assessed using mathematical models. Liver tissue was analyzed for markers of oxidative stress, inflammation, and key regulatory pathways, including NF-κB, Nrf2, MAPKs (JNK and p38), and the IRS1-Akt pathway. We established an effective curcumin dose of 250 mg/kg for 5 days orally. Results demonstrated that after 30 days of exposure, cadmium accumulated in the liver, inducing an oxidative and inflammatory state. This was characterized by increased expression of NF-κB, JNK, and p38, along with diminished Nrf2 expression, hepatic IR, hyperglycemia, and hyperinsulinemia. Curcumin treatment effectively alleviated these metabolic disorders by restoring the balance between NF-κB and Nrf2 in the liver, modulating the MAPK pathway, and, consequently, improving oxidative and inflammatory balance. In conclusion, this study suggests that cadmium induces hepatic IR through an imbalance between NF-κB and Nrf2 signaling pathways. Curcumin treatment appears to improve these pathways, thereby ameliorating hepatic IR.

Inhibition of TREM-1 alleviates neuroinflammation by modulating microglial polarization via SYK/p38MAPK signaling pathway after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI), as a major public health problem, is characterized by high incidence rate, disability rate, and mortality rate. Neuroinflammation plays a crucial role in the pathogenesis of TBI. Triggering receptor expressed on myeloid cells-1 (TREM-1) is recognized as an amplifier of the inflammation in diseases of the central nervous system (CNS). However, the function of TREM-1 remains unclear post-TBI. This study aimed to investigate the function of TREM-1 in neuroinflammation induced by TBI.

METHODS

Brain water content (BWC), modified neurological severity score (mNSS), and Morris Water Maze (MWM) were measured to evaluate the effect of TREM-1 inhibition on nervous system function and outcome after TBI. TREM-1 expression in vivo was evaluated by Western blotting. The cellular localization of TREM-1 in the damaged region was observed via immunofluorescence staining. We also conducted Western blotting to examine expression of SYK, p-SYK and other downstream proteins.

RESULTS

We found that inhibition of TREM-1 reduced brain edema, decreased mNSS and improved neurobehavioral outcomes after TBI. It was further determined that TREM-1 was expressed on microglia and modulated subtype transition of microglia. Inhibition of TREM-1 alleviated neuroinflammation, which was associated with SYK/p38MAPK signaling pathway.

CONCLUSIONS

These findings suggest that TREM-1 can be a potential clinical therapeutic target for alleviating neuroinflammation after TBI.

Michael Acceptors as Anti-Cancer Compounds: Coincidence or Causality?

Michael acceptors represent a class of compounds with potential anti-cancer properties. They act by binding to nucleophilic sites in biological molecules, thereby disrupting cancer cell function and inducing cell death. This mode of action, as well as their ability to be modified and targeted, makes them a promising avenue for advancing cancer therapy. We are investigating the molecular mechanisms underlying Michael acceptors and their interactions with cancer cells, in particular their ability to interfere with cellular processes and induce apoptosis. The anti-cancer properties of Michael acceptors are not accidental but are due to their chemical structure and reactivity. The electrophilic nature of these compounds allows them to selectively target nucleophilic residues on disease-associated proteins, resulting in significant therapeutic benefits and minimal toxicity in various diseases. This opens up new perspectives for the development of more effective and precise cancer drugs. Nevertheless, further studies are essential to fully understand the impact of our discoveries and translate them into clinical practice.

Curcumin in the treatment of inflammation and oxidative stress responses in traumatic brain injury: a systematic review and meta-analysis

Background and aim

Traumatic brain injury (TBI), a leading cause of high morbidity and mortality, represents a significant global public health challenge. Currently, no effective treatment for TBI exists. Curcumin, an active compound extracted from the root of Curcuma longa, has demonstrated neuroprotective properties both in vitro and in vivo. Notably, it has shown potential in reducing oxidative stress and inflammation and enhancing redox balance. This paper conducts a systematic review and meta-analysis to explore curcumin's role in TBI animal models extensively. The findings offer valuable insights for future human clinical trials evaluating curcumin as a therapeutic supplement or nutraceutical in TBI management.

Methods

Comprehensive literature searches were conducted across MEDLINE, Embase, Cochrane, Web of Science, and Google Scholar databases. These searches aimed to identify relevant manuscripts in all languages, utilizing the keywords "curcumin" and "traumatic brain injury."

Results

The final quantitative analysis included 18 eligible articles corresponding to animal studies. The analysis revealed that curcumin significantly reduced inflammatory cytokines, including IL-1β (p = 0.000), IL-6 (p = 0.002), and TNF-α (p = 0.000), across various concentrations, time points, and administration routes. Additionally, curcumin markedly enhanced the activity of oxidative stress markers such as SOD (p = 0.000), Sir2 (p = 0.000), GPx (p = 0.000), and Nrf2 (p = 0.000), while reducing MDA (p = 0.000), 4-HNE (p = 0.001), and oxyprotein levels (p = 0.024). Furthermore, curcumin improved cerebral edema (p = 0.000) and upregulated neuroprotective factors like synapsin I (p = 0.019), BDNF (p = 0.000), and CREB (p = 0.000), without reducing mNSS (p = 0.144). About autophagy and apoptosis, curcumin increased the activity of Beclin-1 (p = 0.000) and Bcl-2 (p = 0.000), while decreasing caspase-3 (p = 0.000), the apoptosis index (p = 0.000), and P62 (p = 0.002).

Conclusion

Curcumin supplementation positively affects traumatic brain injury (TBI) by alleviating oxidative stress and inflammatory responses and promoting neuroprotection. It holds potential as a therapeutic agent for human TBI. However, this conclusion necessitates further substantiation through high-quality literature and additional randomized controlled trials (RCTs).

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/. The registration number of PROSPERO: CRD42023452685.

The effect of curcumin supplementation on circulating adiponectin and leptin concentration in adults: a GRADE-assessed systematic review and meta-analysis of randomised controlled trials

Curcumin is a phytocompound found in the root of turmeric, a common herbal ingredient in many Asian cuisines. The compound contains anti-inflammatory activity, which is mediated through an upregulation of adiponectin and reduction of leptin. Results of randomised controlled trials (RCT) have shown that the effects of curcumin on adipokines are conflicting. Therefore, the current systematic review and meta-analysis of RCT were conducted with the aim of elucidating the role of curcumin supplementation on serum adiponectin and leptin. The search included PubMed, Embase, Cochrane Library, Scopus, Web of Science and Google Scholar from inception to August 2023. For net changes in adipokines, standardised mean differences (SMD) were calculated using random effects models. Thirteen RCT with fourteen treatment arms were eligible for inclusion in this meta-analysis. Curcumin supplementation was effective in increasing serum adiponectin (SMD = 0·86, 95 % CI (0·33, 1·39), P < 0·001; I2 = 93·1 %, P < 0·001) and reducing serum leptin (SMD = -1·42, 95 % CI (-2·29, -0·54), P < 0·001; I2 = 94·7 %, P < 0·001). In conclusion, curcumin supplementation significantly increased circulating adiponectin and decreased leptin levels in adults.

Endoplasmic reticulum stress and the unfolded protein response: emerging regulators in progression of traumatic brain injury

Traumatic brain injury (TBI) is a common trauma with high mortality and disability rates worldwide. However, the current management of this disease is still unsatisfactory. Therefore, it is necessary to investigate the pathophysiological mechanisms of TBI in depth to improve the treatment options. In recent decades, abundant evidence has highlighted the significance of endoplasmic reticulum stress (ERS) in advancing central nervous system (CNS) disorders, including TBI. ERS following TBI leads to the accumulation of unfolded proteins, initiating the unfolded protein response (UPR). Protein kinase RNA-like ER kinase (PERK), inositol-requiring protein 1 (IRE1), and activating transcription factor 6 (ATF6) are the three major pathways of UPR initiation that determine whether a cell survives or dies. This review focuses on the dual effects of ERS on TBI and discusses the underlying mechanisms. It is suggested that ERS may crosstalk with a series of molecular cascade responses, such as mitochondrial dysfunction, oxidative stress, neuroinflammation, autophagy, and cell death, and is thus involved in the progression of secondary injury after TBI. Hence, ERS is a promising candidate for the management of TBI.

The effect and mechanism of novel methoxy curcumin analogs based on network pharmacology

In this study, a series of novel compounds were synthesized by introducing the 3,4,5-trimethoxyphenyl and isatin groups into the monocarbonyl skeleton of curcumin. The possible biological activities and potential targets for these compounds were explored through network pharmacology. The results revealed that these compounds could significantly inhibit production of the inflammatory factors IL-6 and TNF-α, and suppress phosphorylation of the extracellular signal-regulated kinase (ERK) protein. Moreover, molecular docking experiments showed that the ERK protein was the potential target for these compounds. In summary, this study, through network pharmacology, presents a novel series of methoxy curcumin analogs as potent anti-inflammatory drugs.

Curcumin and analogues in mitigating liver injury and disease consequences: From molecular mechanisms to clinical perspectives

BACKGROUND

Liver injury is a prevalent global health concern, impacting a substantial number of individuals and leading to elevated mortality rates and socioeconomic burdens. Traditional primary treatment options encounter resource constraints and high costs, prompting exploration of alternative adjunct therapies, such as phytotherapy. Curcumin demonstrates significant therapeutic potential across various medical conditions, particularly emerging as a promising candidate for liver injury treatment.

PURPOSE

This study aims to provide current evidence maps of curcumin and its analogs in the context of liver injury, covering aspects of biosafety, toxicology, and clinical trials. Importantly, it seeks to summarize the intricate mechanisms modulated by curcumin.

METHODS

We conducted a comprehensive search of MEDLINE, Web of Science, and Embase up to July 2023. Titles and abstracts were reviewed to identify studies that met our eligibility criteria. The screening process involved three authors independently assessing the potential of curcumin mitigating liver injury and its disease consequences by reviewing titles, abstracts, and full texts.

RESULTS

Curcumin and its analogs have demonstrated low toxicity in vitro and in vivo. However, the limited bioavailability has hindered their advanced use in liver injury. This limitation can potentially be addressed by nano-curcumin and emerging drug delivery systems. Curcumin plays a role in alleviating liver injury by modulating the antioxidant system, as well as cellular and molecular pathways. The specific mechanisms involve multiple pathways, such as NF-κB, p38/MAPK, and JAK2/STAT3, and the pro-apoptosis Bcl-2/Bax/caspase-3 axis in damaged cells. Additionally, curcumin targets nutritional metabolism, regulating the substance in liver cells and tissues. The microenvironment associated with liver injury, like extracellular matrix and immune cells and factors, is also regulated by curcumin. Initial evaluation of curcumin and its analogs through 12 clinical trials demonstrates their potential application in liver injury.

CONCLUSION

Curcumin emerges as a promising phytomedicine for liver injury owing to its effectiveness in hepatoprotection and low toxicity profile. Nevertheless, in-depth investigations are warranted to unravel the complex mechanisms through which curcumin influences liver tissues and overall physiological milieu. Moreover, extensive clinical trials are essential to determine optimal curcumin dosage forms, maximizing its benefits and achieving favorable clinical outcomes.

Nanocarrier-mediated curcumin delivery: An adjuvant strategy for CNS disease treatment

Neurological disorders are a major global challenge, which counts for a substantial slice of disease burden around the globe. In these, the challenging landscape of central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and neuro-AIDS, demands innovative and novel therapeutic approaches. Curcumin, a versatile natural compound with antioxidant and anti-inflammatory properties, shows great potential as a CNS adjuvant therapy. However, its limited bioavailability and suboptimal permeability to the blood-brain barrier (BBB) hamper the therapeutic efficacy of curcumin. This review explores how nanocarrier facilitates curcumin delivery, which has shown therapeutic efficacy for various non-CNS diseases, for example, cancers, and can also revolutionize the treatment outcomes in patients with CNS diseases. Toward this, intranasal administration of curcumin as a non-invasive CNS drug delivery route can also aid its therapeutic outcomes as an adjuvant therapy for CNS diseases. Intranasal delivery of nanocarriers with curcumin improves the bioavailability of curcumin and its BBB permeability, which is instrumental in promoting its therapeutic potential. Furthermore, curcumin's inhibitory effect on efflux transporters will help to enhance the BBB and cellular permeability of various CNS drugs. The therapeutic potential of curcumin as an adjuvant has the potential to yield synergistic effects with CNS drugs and will help to reduce CNS drug doses and improve their safety profile. Taken together, this approach holds a promise for reshaping CNS disease management by maximizing curcumin's and other drugs' therapeutic benefits.

Impact of curcumin on p38 MAPK: therapeutic implications

Curcumin (diferuloylmethane) is a herbal remedy which possesses numerous biological attributes including anti-inflammatory, anti-oxidant and anti-cancer properties. Curcumin has been shown to impact a number of signaling pathways including nuclear factor kappa B (NF-KB), reactive oxygen species (ROS), Wingless/Integrated (Wnt), Janus kinase-signal transducer and activator of mitogen-activated protein kinase (MAPK) and transcription (JAK/STAT). P38 belongs to the MAPKs, is known as a stress-activated MAPK and is involved in diverse biological responses. P38 is activated in various signaling cascades. P38 plays a role in inflammation, cell differentiation, proliferation, motility and survival. This cascade can serve as a therapeutic target in many disorders. Extensive evidence confirms that curcumin impacts the P38 MAPK signaling pathway, through which it exerts anti-inflammatory, neuroprotective, and apoptotic effects. Hence, curcumin can positively affect inflammatory disorders and cancers, as well as to increase glucose uptake in cells. This review discusses the pharmacological and therapeutic effects of curcumin as effected through p38 MAPK.

Progress on the Extraction, Separation, Biological Activity, and Delivery of Natural Plant Pigments

Natural plant pigments are safe and have low toxicity, with various nutrients and biological activities. However, the extraction, preservation, and application of pigments are limited due to the instability of natural pigments. Therefore, it is necessary to examine the extraction and application processes of natural plant pigments in detail. This review discusses the classification, extraction methods, biological activities, and modification methods that could improve the stability of various pigments from plants, providing a reference for applying natural plant pigments in the industry and the cosmetics, food, and pharmaceutical industries.

MPC-n (IgG) improves long-term cognitive impairment in the mouse model of repetitive mild traumatic brain injury

BACKGROUND

Contact sports athletes and military personnel who suffered a repetitive mild traumatic brain injury (rmTBI) are at high risk of neurodegenerative diseases such as advanced dementia and chronic traumatic encephalopathy (CTE). However, due to the lack of specific biological indicators in clinical practice, the diagnosis and treatment of rmTBI are quite limited.

METHODS

We used 2-methacryloyloxyethyl phosphorylcholine (MPC)-nanocapsules to deliver immunoglobulins (IgG), which can increase the delivery efficiency and specific target of IgG while reducing the effective therapeutic dose of the drug.

RESULTS

Our results demonstrated that MPC-capsuled immunoglobulins (MPC-n (IgG)) significantly alleviated cognitive impairment, hippocampal atrophy, p-Tau deposition, and myelin injury in rmTBI mice compared with free IgG. Furthermore, MPC-n (IgG) can also effectively inhibit the activation of microglia and the release of inflammatory factors.

CONCLUSIONS

In the present study, we put forward an efficient strategy for the treatment of rmTBI-related cognitive impairment and provide evidence for the administration of low-dose IgG.

Inflammaging, cellular senescence, and cognitive aging after traumatic brain injury

Traumatic brain injury (TBI) is associated with mortality and morbidity worldwide. Accumulating pre-clinical and clinical data suggests TBI is the leading extrinsic cause of progressive neurodegeneration. Neurological deterioration after either a single moderate-severe TBI or repetitive mild TBI often resembles dementia in aged populations; however, no currently approved therapies adequately mitigate neurodegeneration. Inflammation correlates with neurodegenerative changes and cognitive dysfunction for years post-TBI, suggesting a potential association between immune activation and both age- and TBI-induced cognitive decline. Inflammaging, a chronic, low-grade sterile inflammation associated with natural aging, promotes cognitive decline. Cellular senescence and the subsequent development of a senescence associated secretory phenotype (SASP) promotes inflammaging and cognitive aging, although the functional association between senescent cells and neurodegeneration is poorly defined after TBI. In this mini-review, we provide an overview of the pre-clinical and clinical evidence linking cellular senescence with poor TBI outcomes. We also discuss the current knowledge and future potential for senotherapeutics, including senolytics and senomorphics, which kill and/or modulate senescent cells, as potential therapeutics after TBI.

Therapy of traumatic brain injury by modern agents and traditional Chinese medicine

Traumatic brain injury (TBI) is the leading cause of disability and death, and the social burden of mortality and morbidity caused by TBI is significant. Under the influence of comprehensive factors, such as social environment, lifestyle, and employment type, the incidence of TBI continues to increase annually. Current pharmacotherapy of TBI mainly focuses on symptomatic supportive treatment, aiming to reduce intracranial pressure, ease pain, alleviate irritability, and fight infection. In this study, we summarized numerous studies covering the use of neuroprotective agents in different animal models and clinical trials after TBI. However, we found that no drug has been approved as specifically effective for the treatment of TBI. Effective therapeutic strategies for TBI remain an urgent need, and attention is turning toward traditional Chinese medicine. We analyzed the reasons why existing high-profile drugs had failed to show clinical benefits and offered our views on the research of traditional herbal medicine for treating TBI.

Low curcumin concentrations combined with blue light inhibits cutibacterium acnes biofilm-induced inflammatory response through suppressing MAPK and NF-κB in keratinocytes

BACKGROUND

Curcumin has been employed as a photosensitizer agent during photodynamic therapy (PDT). Cutibacterium acnes (C. acnes) can cause an inflammatory response in human keratinocytes; however, no research has been conducted to determine whether curcumin and its photodynamic properties can prevent this inflammatory reaction.

OBJECTIVE

We hypothesized that curcumin may control the C. acnes biofilm-induced inflammatory response in keratinocytes, either alone or in combination with blue light photodynamic therapy.

METHODS

Following C. acnes biofilm stimulation, human primary keratinocytes were treated with 20 μM curcumin solution alone or 5 μM curcumin with combined blue light irradiation. The amount of secreted protein was measured using an ELISA kit. The expression levels of Toll-like receptor 2 (TLR2) and its downstream proteins were determined using western blot.

RESULTS

Treatment with 20 μM curcumin, but not 5 μM curcumin, reduced the inflammatory response to C. acnes biofilms in keratinocytes by blocking the TLR2/MAPK/NF-κB pathway. Interestingly, 5 μM curcumin combined with blue light also reduced the C. acnes biofilm-induced inflammation indicated above by blocking the TLR2/MAPK/NF-κB pathway.

CONCLUSION

Curcumin alone, in sufficient concentrations, or low-concentration curcumin with blue light had anti-inflammatory activity on keratinocytes stimulated by C. acnes biofilms through inhibition of MAPK and NF-κB signaling pathways by downregulating TLR2 expression.

Exosomes derived from bone marrow mesenchymal stem cells attenuate neurological damage in traumatic brain injury by alleviating glutamate-mediated excitotoxicity

BACKGROUND

Traumatic brain injury (TBI) is one of the major contributors to disability and death worldwide. Glutamate-mediated excitotoxicity, one of the secondary injuries occurring after TBI, leads to extreme neuronal apoptosis, and can be a potential target for intervention. Bone marrow mesenchymal stem cells-derived exosomes (BMSCs-Exos) have demonstrated neuroprotective effects on TBI. However, their precise role and the underlying mechanism by which they regulate glutamate-mediated excitotoxicity have not yet been determined. Therefore, this study aimed to determine whether BMSCs-Exos alleviate glutamate excitotoxicity post-TBI and their associated mechanism.

METHODS

BMSCs-Exos were extracted from the BMSCs incubation medium and identified by transmission electron microscopy, nanoparticle trafficking analysis, and western blotting. The neuroprotective effects of BMSCs-Exos on glutamate excitotoxicity were investigated in the glutamate-mediated excitotoxicity neuronal cell model and the TBI rat model (TBI induced by controlled cortical impact) using western blotting and TUNEL assay. Cortical lesion samples were collected post-TBI on day-1 and day-14 to study histology. In addition, cortical lesion volume on days 1, 3 and 7 following TBI was determined using T2-weighted magnetic resonance imaging (MRI), and cognitive function was assessed at 4 weeks following TBI using the Morris water maze (MWM) test.

RESULTS

BMSC-Exos were observed to be spherical with a mean diameter of 109.9 nm, and expressed exosomal markers CD9, CD81 and TSg101. BMSCs-Exos were efficiently endocytosed by astrocytes after co-incubation for 24 h. In vitro studies revealed that 125 μM of glutamate significantly induced neuronal apoptosis, which was attenuated by BMSCs-Exos in astrocyte-neuron co-cultures. This attenuation was mediated by the upregulation of glutamate transporter-1 (GLT-1) level and the downregulation of p-p38 MAPK level in astrocytes. Similar results were obtained in vivo, wherein we verified that PKH67-labeled BMSCs-Exos administered intravenously could reach the perilesional cortex crossing the blood-brain barrier and significantly reduce glutamate levels in the perilesional cortex of the TBI rat, accompanied by increased GLT-1 level and downregulation in p-p38 MAPK level. Additionally, western blotting and TUNEL staining also revealed that BMSCs-Exos significantly downregulated the expression of pro-apoptosis markers, including cleaved caspase-3 and cleaved caspase-9, and attenuated neuronal apoptosis following TBI. Immunohistochemical analysis and Nissl staining showed that BMSCs-Exos significantly increased GLT-1-positive cells, and the number of apoptotic neurons decreased in the perilesional cortex. Moreover, MRI and MWM results revealed that BMSCs-Exos significantly minimized cortical lesion volume and ameliorated cognitive function after TBI. The underlying neuroprotective mechanism of BMSCs-Exos may be due to an increase in GLT-1 level in astrocytes by blocking the p38 MAPK signaling pathway.

CONCLUSION

Taken together, our findings demonstrate that the implementation of BMSCs-Exos may be an effective prospective therapy for attenuating post-TBI neurological damage.

How Curcumin Targets Inflammatory Mediators in Diabetes: Therapeutic Insights and Possible Solutions

Diabetes mellitus is a multifactorial chronic metabolic disorder, characterized by altered metabolism of macro-nutrients, such as fats, proteins, and carbohydrates. Diabetic retinopathy, diabetic cardiomyopathy, diabetic encephalopathy, diabetic periodontitis, and diabetic nephropathy are the prominent complications of diabetes. Inflammatory mediators are primarily responsible for these complications. Curcumin, a polyphenol derived from turmeric, is well known for its anti-oxidant, anti-inflammatory, and anti-apoptotic properties. The regulation of several signaling pathways effectively targets inflammatory mediators in diabetes. Curcumin’s anti-inflammatory and anti-oxidative activities against a wide range of molecular targets have been shown to have therapeutic potential for a variety of chronic inflammatory disorders, including diabetes. Curcumin’s biological examination has shown that it is a powerful anti-oxidant that stops cells from growing by releasing active free thiol groups at the target location. Curcumin is a powerful anti-inflammatory agent that targets inflammatory mediators in diabetes, and its resistant form leads to better therapeutic outcomes in diabetes complications. Moreover, Curcumin is an anti-oxidant and NF-B inhibitor that may be useful in treating diabetes. Curcumin has been shown to inhibit diabetes-related enzymes, such as a-glucosidase, aldose reductase and aldose reductase inhibitors. Through its anti-oxidant and anti-inflammatory effects, and its suppression of vascular endothelial development and nuclear transcription factors, curcumin has the ability to prevent, or reduce, the course of diabetic retinopathy. Curcumin improves insulin sensitivity by suppressing phosphorylation of ERK/JNK in HG-induced insulin-resistant cells and strengthening the PI3K-AKT-GSK3B signaling pathway. In the present article, we aimed to discuss the anti-inflammatory mechanisms of curcumin in diabetes regulated by various molecular signaling pathways.