Effects of carbocisteine on altered activities of glycosidase and glycosyltransferase and expression of Muc5ac in SO2-exposed rats

Carbocisteine as a Modulator of Nrf2/HO-1 and NFκB Interplay in Rats: New Inspiration for the Revival of an Old Drug for Treating Ulcerative Colitis

Ulcerative colitis (UC), an inflammatory bowel disease, is a chronic condition of a multifaceted pathophysiology. The incidence of UC is increasing internationally. The current therapies for UC lack relative effectiveness and are associated with adverse effects. Therefore, novel therapeutic options should be developed. It has been well documented that modulating the Nrf2/NFκB is a promising therapeutic target in inflammation. Carbocisteine is a mucoregulatory medication and its efficacy in COPD was found to be more closely related to its antioxidant and anti-inflammatory properties. Carbocisteine has not yet been examined for the management of UC. Hence, our approach was to investigate the potential coloprotective role of carbocisteine in acetic acid-induced colitis in rats. Our results revealed that carbocisteine improved colon histology and macroscopic features and subdued the disease activity as well. Additionally, carbocisteine attenuated colon shortening and augmented colon antioxidant defense mechanisms via upregulating catalase and HO-1 enzymes. The myeloperoxidase activity was suppressed indicating inhibition of the neutrophil infiltration and activation. Consistent with these findings, carbocisteine boosted Nrf2 expression along with NFκB inactivation. Consequently, carbocisteine downregulated the proinflammatory cytokines IL-6 and TNF-α and upregulated the anti-inflammatory cytokine IL-10. Concomitant to these protective roles, carbocisteine displayed anti-apoptotic properties as revealed by the reduction in the Bax: BCL-2 ratio. In conclusion, carbocisteine inhibited oxidative stress, inflammatory response, and apoptosis in acetic acid-induced UC by modulating the Nrf2/HO-1 and NFκB interplay in rats. Therefore, the current study provides a potential basis for repurposing a safe and a commonly used mucoregulator for the treatment of UC.

Clinical Efficacy of Carbocysteine in COPD: Beyond the Mucolytic Action

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease with a versatile and complicated profile, being the fourth most common single cause of death worldwide. Several research groups have been trying to identify possible therapeutic approaches to treat COPD, such as the use of mucoactive drugs, which include carbocysteine. However, their role in the treatment of patients suffering from COPD remains controversial due to COPD's multifaceted profile. In the present review, 72 articles, published in peer-reviewed journals with high impact factors, are analyzed in order to provide significant insight and increase the knowledge about COPD considering the important contribution of carbocysteine in reducing exacerbations via multiple mechanisms. Carbocysteine is in fact able to modulate mucins and ciliary functions, and to counteract viral and bacterial infections as well as oxidative stress, offering cytoprotective effects. Furthermore, carbocysteine improves steroid responsiveness and exerts anti-inflammatory activity. This analysis demonstrates that the use of carbocysteine in COPD patients represents a well-tolerated treatment with a favorable safety profile, and might contribute to a better quality of life for patients suffering from this serious illness.

Immunomodulatory Effects of Ambroxol on Airway Hyperresponsiveness and Inflammation

Ambroxol is used in COPD and asthma to increase mucociliary clearance and regulate surfactant levels, perhaps through anti-oxidant and anti-inflammatory activities. To determine the role and effect of ambroxol in an experimental model of asthma, BALB/c mice were sensitized to ovalbumin (OVA) followed by 3 days of challenge. Airway hyperresponsiveness (AHR), lung cell composition and histology, and cytokine and protein carbonyl levels in bronchoalveolar lavage (BAL) fluid were determined. Ambroxol was administered either before the first OVA challenge or was begun after the last allergen challenge. Cytokine production levels from lung mononuclear cells (Lung MNCs) or alveolar macrophages (AM) were also determined. Administration of ambroxol prior to challenge suppressed AHR, airway eosinophilia, goblet cell metaplasia, and reduced inflammation in subepithelial regions. When given after challenge, AHR was suppressed but without effects on eosinophil numbers. Levels of IL-5 and IL-13 in BAL fluid were decreased when the drug was given prior to challenge; when given after challenge, increased levels of IL-10 and IL-12 were detected. Decreased levels of protein carbonyls were detected in BAL fluid following ambroxol treatment after challenge. In vitro, ambroxol increased levels of IL-10, IFN-γ, and IL-12 from Lung MNCs and AM, whereas IL-4, IL-5, and IL-13 production was not altered. Taken together, ambroxol was effective in preventing AHR and airway inflammation through upregulation of Th1 cytokines and protection from oxidative stress in the airways.

Synthesis, chemical identification, antioxidant capacities and immunological evaluation studies of a novel silver(I) carbocysteine complex

A new silver-carbocysteine (Ccy-Ag) complex [Ag2(Ccy)2(H2O)2] has been synthesized and characterized by using a combination of FTIR, Raman, molar conductivity, (1)H NMR, electronic spectra, thermal analyses, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The infrared spectrum of Ccy-Ag complex in comparison with carbocysteine ligand prove that Ccy behaves as monobasic bidentate chelate to the silver metal ions via the deprotonated carboxylate O atom. The assessments of Ccy and its complexation with Ag(+) in treating COPD, evaluating immune activities through measuring IL-8, TGF-β1, VEGF and TNF-α, antioxidant activities of (Ccy-Ag) complex by measuring SOD, MDA and GPX and bronchial asthma were discussed.

Effect of Curculigo orchioides on reflux esophagitis by suppressing proinflammatory cytokines

This study was performed to investigate effects of Curculigo orchioides rhizome (curculiginis rhizome) on acute reflux esophigitis (RE) in rats that are induced by pylorus and forestomach ligation operation. Proinflammatory cytokine, as well as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were all assayed and the expression of TNF-α and COX2 analyzed by RT-PCR. The esophagic tissue damage of reflux esophagitis rat was increased compared to that of normal intact group. However, the esophagic damage percentage from the extract of curculiginis rhizoma (ECR) 600 mg/kg and ECR 300 mg/kg were significantly lower than that of the RE control group. Administration of α-tocopherol (30 mg/kg) and ECR (600 mg/kg, 300 mg/kg, and 150 mg/kg) had a significant effect on the gastric acid pH in rats with induced reflux esophagitis (p < 0.05). The treatment with ECR significantly reduced the production of cytokines TNF-α, IL-1β and IL-6 levels compared to the model group (p < 0.05). The expression of TNF-α and COX2 in the intact esophageal mucosa was low while those of the RE control group were significantly higher due to an inflammatory reaction in the esophagus. Compare to the model group, treatment with α-tocopherol or ECR significantly inhibited the expression levels of COX2 and TNF-α in a dose-dependent manner. These results suggest that anti-inflammatory and protective effects of ECR could attenuate the severity of reflux esophagitis and prevent esophageal mucosal damage.

Low-methoxyl pectin stimulates small intestinal mucin secretion irrespective of goblet cell proliferation and is characterized by jejunum Muc2 upregulation in rats

Generally, soluble fibers increase small intestinal mucin secretion by increasing the number of goblet cells in a viscosity-dependent manner. The present study aimed to examine the mechanism by which low-methoxyl pectin (LPC) affects mucin secretion in the small intestine. First, diets containing 50 g/kg of low-viscosity fiber (LPC, gum arabic, guar gum, low-molecular konjac mannan, arabinogalactan, sodium alginate) or high-molecular konjac mannan (KMH) were fed to Wistar rats for 10 d. Luminal mucin was greater in the LPC and KMH groups than in the fiber-free control group, but only the KMH group had more goblet cells in the ileum compared with the other groups. Next, Sprague-Dawley rats were fed LPC, KMH, or high-methoxyl pectin (HPC) diets (50 g/kg) for 10 d. The KMH and LPC groups, but not the HPC group, had greater luminal mucin than the control group, whereas jejunum Muc2 expression was higher only in the LPC group. Sprague-Dawley rats fed the LPC diet for 1 or 3 d had greater luminal mucin and jejunum Muc2 expression than those fed the control diet. In vitro studies using HT-29MTX cells showed that, of the various fibers studied, only LPC and HPC affected mucin secretion. Finally, Wistar rats were fed the LPC diet with or without neomycin in drinking water for 10 d; neomycin treatment did not compromise the effect of LPC on mucin secretion. We conclude that LPC does not affect the number of goblet cells but can interact directly with the epithelium and stimulate small intestinal mucin secretion.

Resveratrol inhibits mucin gene expression, production and secretion from airway epithelial cells

The study investigated whether resveratrol significantly affects mucin gene expression, production and secretion from airway epithelial cells. Confluent NCI-H292 cells were pretreated with resveratrol for 30 min and then stimulated with EGF (epidermal growth factor), PMA (phorbol 12-myristate 13-acetate) and TNF-α (tumor necrosis factor-α) for 24 h, respectively. The MUC5AC gene expression and mucin protein production were measured by RT-PCR and ELISA. The effect of resveratrol on TNF-α- or PMA-induced activation of NF-κB p65 was also examined. Confluent primary rat tracheal surface epithelial (RTSE) cells were pretreated with adenosine triphosphate (ATP) for 5 min and then treated for 30 min in the presence of resveratrol to assess the effect on mucin secretion using ELISA. The results were as follows: (1) resveratrol inhibited the expression of MUC5AC gene induced by EGF or PMA or TNF-α from NCI-H292 cells; (2) resveratrol also inhibited the production of MUC5AC mucin protein induced by the same inducers from NCI-H292 cells; (3) resveratrol inhibited the activation of NF-κB p65 by TNF-α or PMA in NCI-H292 cells; (4) resveratrol significantly decreased ATP-induced mucin secretion from cultured RTSE cells. This result suggests that resveratrol can regulate mucin gene expression, production and secretion, by directly acting on airway epithelial cells.

Carbocisteine promotes phagocytosis of apoptotic cells by alveolar macrophages

Clearance of apoptotic cells, so-called efferocytosis, by alveolar macrophages (AMs) is important for lung homeostasis and is impaired in pulmonary inflammatory diseases, such as chronic obstructive pulmonary disease and asthma. Carbocisteine, a mucoregulatory drug, corrects the contents of fucose in airway mucus and has anti-inflammatory properties in airway inflammation. Thus, we conducted the present study to better understand the anti-inflammatory properties of carbocisteine. First, we induced airway inflammation in mice with lipopolysaccharide intratracheally. Carbocisteine significantly decreased neutrophil numbers in bronchoalveolar lavage fluid at the resolution phase of inflammation, implying the promotion of neutrophil clearance. Then, we investigated whether carbocisteine would enhance the efferocytosis by AMs isolated from mice and found that this drug promoted not only the phagocytosis but also the binding of apoptotic cells to AMs in vitro. Furthermore, carbocisteine decreased the fucose residues stained with fluorescent fucose-binding lectin, Lens culinaris agglutinin, on the cell surface of AMs. We found here that removing fucose residues from cell surfaces of AMs by fucosidase markedly enhanced both the binding and phagocytosis of apoptotic cells. Finally, AMs from mice orally given carbocisteine also promoted both the binding and phagocytosis ex vivo similarly to in vitro. These results suggest that carbocisteine could promote the clearance of apoptotic cells by AMs in airway. In addition, the present findings suggest that the binding and phagocytosis of apoptotic cells may be modulated by fucose residues on the cell surface of AMs.

Downregulation of mucins in graft bile ducts after liver transplantation in rats

BACKGROUND

Nonanastomotic biliary strictures represent a serious complication after orthotopic liver transplantation (OLT). This study investigates the potential role of mucins in bile duct injury after OLT.

METHODS

Sprague-Dawley rats were divided into four groups: normal group (Normal, n=5), sham-operated group (Sham, n=20), OLT group with 1 hr donor cold ischemic time (n=20), and OLT group with 12 hr donor cold ischemic time (OLTn=20). Expression of mucins and GATA factors in bile ducts was examined by real-time polymerase chain reaction, immunohistochemistry, and immunoblotting. Bile was collected for biochemical analysis, and the histological changes associated with bile duct injury were evaluated.

RESULTS

In normal bile ducts, Muc1, Muc2, Muc3A, Muc4, and Muc6 mRNA were expressed, whereas Muc5AC mRNA was undetectable. The expression of Muc1, Muc3A, and Muc4 but not Muc2 and Muc6 at mRNA level in graft bile ducts decreased remarkably early after OLT. The decreased expression of Muc1 and Muc4 was further confirmed at protein level by immunohistochemistry and immunoblotting. Downregulation of Muc1 and Muc3A expression by prolonged cold ischemic time was significantly associated with the injury severity scores of large but not small bile ducts. Among six GATA factors, GATA3, GATA4, and GATA6 mRNA were expressed in normal bile ducts. GATA4 and GATA6 mRNA levels decreased significantly after OLT.

CONCLUSION

Downregulation of Muc1 and Muc3A expression by prolonged cold ischemic time may play a potential role in large bile duct injury early after OLT.

Inhibition of secretion, production and gene expression of mucin from cultured airway epithelial cells by prunetin

This study investigated whether prunetin significantly affects the secretion, production and gene expression of mucin from cultured airway epithelial cells. Confluent primary rat tracheal surface epithelial (RTSE) cells were pretreated with adenosine triphosphate (ATP) for 5 min and then chased for 30 min in the presence of prunetin to assess the effect on mucin secretion using enzyme-linked immunosorbent assay (ELISA). At the same time, confluent NCI-H292 cells were pretreated with prunetin for 30 min and then stimulated with epidermal growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA) for 24 h, respectively. The MUC5AC mucin gene expression and mucin protein production were measured by reverse transcription-polymerase chain reaction (RT-PCR) and ELISA. The results were as follows: (1) prunetin significantly suppressed ATP-induced mucin secretion from cultured RTSE cells; (2) prunetin inhibited the production of MUC5AC mucin protein induced by EGF or PMA from NCI-H292 cells; (3) prunetin also inhibited the expression of MUC5AC mucin gene induced by EGF or PMA from NCI-H292 cells. This result suggests that prunetin can regulate the secretion, production and gene expression of mucin, by directly acting on airway epithelial cells.

Effects of combination therapy with montelukast and carbocysteine in allergen-induced airway hyperresponsiveness and airway inflammation

BACKGROUND AND PURPOSE

Montelukast and S-carbocysteine have been used in asthmatic patients as an anti-inflammatory or mucolytic agent respectively. S-carbocysteine also exhibits anti-inflammatory properties.

EXPERIMENTAL APPROACH

Ovalbumin (OVA) sensitized BALB/c mice were challenged with OVA for 3 days followed by single OVA re-challenge (secondary challenge) 2 weeks later. Forty-eight hours after secondary challenge, mice were assessed for airway hyperresponsiveness (AHR) and cell composition in bronchoalveolar lavage (BAL) fluid. Suboptimal doses of 10 mg.kg(-1) of S-carbocysteine by intraperitoneal injection (ip), 20 mg.kg(-1) of montelukast by gavage, the combination of S-carbocysteine and montelukast or 3 mg.kg(-1) of dexamethasone as a control were administered from 1 day before the secondary challenge to the last experimental day. Isolated lung cells were cultured with OVA and montelukast to determine the effects on cytokine production.

KEY RESULTS

Treatment with S-carbocysteine or montelukast reduced both AHR and the numbers of eosinophils in BAL fluid. Neutralizing IFN-gamma abolished the effects of S-carbocysteine on these airway responses. Combination of the two drugs showed further decreases in both AHR and eosinophils in the BAL fluid. Goblet cell metaplasia and Th2-type cytokines, interleukin (IL)-4, IL-5 and IL-13, in BAL fluid were decreased with montelukast treatment. Conversely, S-carbocysteine increased Th1-type cytokines, IFN-gamma and IL-12 in BAL fluid.

CONCLUSIONS AND IMPLICATIONS

The combination of two agents, montelukast and S-carbocysteine, demonstrated additive effects on AHR and airway inflammation in a secondary allergen model most likely through independent mechanisms of action.

Daidzein regulates secretion, production and gene expression of mucin from airway epithelial cells stimulated by proinflammatory factor and growth factor

In this study, we investigated whether daidzein significantly affects secretion, production and gene expression of mucin from cultured airway epithelial cells. Confluent primary rat tracheal surface epithelial (RTSE) cells were pretreated with adenosine triphosphate (ATP) for 5 min and then chased for 30 min in the presence of daidzein to assess the effect on mucin secretion using ELISA. At the same time, confluent NCI-H292 cells were pretreated with daidzein for 30 min and then stimulated with EGF and PMA for 24 h, respectively. The MUC5AC mucin gene expression and mucin protein production were measured by RT-PCR and ELISA. The results were as follows: (1) daidzein significantly decreased ATP-induced mucin secretion from cultured RTSE cells; (2) daidzein inhibited the production of MUC5AC mucin protein induced by EGF or PMA from NCI-H292 cells; (3) daidzein also inhibited the expression of MUC5AC mucin gene induced by EGF or PMA from NCI-H292 cells. This result suggests that daidzein can regulate secretion, production and gene expression of mucin, by directly acting on airway epithelial cells.

Protective effects of salicylic acid and vitamin C on sulfur dioxide-induced lipid peroxidation in mice

The antioxidant effects of exogenous salicylic acid (SA) and vitamin C (Vit C) on the oxidative stress induced by 56 mg/m(3) of sulfur dioxide (SO2) in mouse livers and brains were investigated. The exposure of SO2 caused significant elevation of thiobarbituric acid-reactive substance (TBARS) levels and reduction of enzyme activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in brain and liver, accompanied by a decrease in relative growth rate, when compared with controls. Application of moderate concentrations of SA and Vit C markedly reduced the SO2-induced elevation of TBARS levels, with 5.5 mg/kg SA or 200 mg/kg Vit C being most effective. In contrast to the decrease of TBARS levels, the levels of SOD, POD, and CAT in liver and brain were significantly increased in comparison with controls. The polyacrylamide gel electrophoresis (PAGE) of total liver proteins showed that the SO2 inhalation caused a 30-kD protein band disappearance compared with the control. However, the band remained unchanged in the samples treated with 5.5 and 8.25 mg/kg SA or 100, 200, and 400 mg/kg Vit C. Therefore, this protein band may serve as a marker for the damage induced by SO2 and an additional basis for drug screening and selection.

Preferential reduction of the α-2-6-sialylation from cell surface N-glycans of human diploid fibroblastic cells by in vitro aging

Human diploid fibroblastic cell line, TIG-3, has a finite life span of about 80 population doubling levels (PDL), and is used for in vitro aging studies. Young cells (PDL 23) grew to higher cell densities at a higher growth rate than aged cells (PDL 77). When the electrophoretic mobility of cells was determined, the negative surface charge of the aged cells decreased significantly when compared to that of young cells. Lectin blot analysis of membrane glycoproteins showed that the alpha-2-6-sialylation but not the alpha-2-3-sialylation of N-glycans decreases markedly in the aged cells when compared to the young cells. In support of this observation, the cDNA microarray assay and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the gene expression of the alpha-2,6-sialyltransferase I (ST6Gal I), which transfers sialic acid to galactose residues of N-glycans, decreases in the aged cells. These results indicate that the concordant decrease of the alpha-2,6-sialylation of N-glycans with the ST6Gal I gene expression is induced in TIG-3 cells by in vitro aging.

Effects of carbocisteine on sialyl-Lewis x expression in an airway carcinoma cell line stimulated with tumor necrosis factor-alpha

Carbocisteine is a mucoregulatory drug normalizing sialic acid and fucose contents in mucins through the regulation of glycosyltransferase activities. Tumor necrosis factor (TNF)-alpha-induced overexpression of sialyl-Lewis x epitopes, containing sialic acid and fucose, in mucins were previously reported to be regulated by glycosyltransferase mRNAs expression through phosphatidyl inositol-specific phospholipase C (PI-PLC) signaling pathways [Ishibashi, Y., Inouye, Y., Okano, T., Taniguchi, A., 2005. Regulation of sialyl-Lewis x epitope expression by TNF-alpha and EGF in an airway carcinoma cell line. Glycoconj. J. 22, 53-62]. To investigate the mechanism behind the mucoregulatory action of carbocisteine, the present study evaluated the effects of carbocisteine on TNF-alpha-induced overexpression of sialyl-Lewis x epitopes in NCI-H292 cells. 100 mug/ml of carbocisteine was able to inhibit the TNF-alpha-induced expression of hST3GallV mRNA, FUT3 mRNA, C2/4GnT mRNA and sialyl-Lewis x epitopes as well as the TNF-alpha-induced activity of PI-PLC in NCI-H292 cells. These findings suggest that carbocisteine may normalize the sialyl-Lewis x epitopes expression in mucins through the inhibition of cellular PI-PLC activity in vivo.

S-CMC-Lys-dependent stimulation of electrogenic glutathione secretion by human respiratory epithelium

Glutathione (GSH) is one of the most important defense mechanisms against oxidative stress in the respiratory epithelial lining fluid. Considering that GSH secretion in respiratory cells has been postulated to be at least partially electrogenic, and that the mucoregulator S-carbocysteine lysine salt monohydrate (S-CMC-Lys) can cause an activation of epithelial Cl(-) conductance, the purpose of this study was to verify whether S-CMC-Lys is able to stimulate GSH secretion. Experiments have been performed by patch-clamp technique, by high-performance liquid chromatography (HPLC) assay, and by Western blot analysis on cultured lines of human respiratory cells (WI-26VA4 and CFT1-C2). In whole-cell configuration, after cell exposure to 100 microM S-CMC-Lys, a current due to an outward GSH flux was observed, which was inhibitable by 5-nitro-2-(3-phenylpropylamino)-benzoate and glibenclamide. This current was not observed in CFT1-C2 cells, where a functional cystic fibrosis transmembrane conductance regulator (CFTR) is lacking. Inside-out patch-clamp experiments (GSH on the cytoplasm side, Cl(-) on the extracellular side) showed the activity of a channel, which was able to conduct current in both directions: the single channel conductance was 2-4 pS, and the open probability (P(o)) was low and voltage-independent. After preincubation with 100 microM S-CMC-Lys, there was an increase in P(o), in the number of active channels present in each patch, and in the relative permeability to GSH vs Cl(-). Outwardly directed efflux of GSH could also be increased by protein kinase A, adenosine 5'-triphosphate, and cyclic adenosine monophosphate (cAMP) added to the cytoplasmic side (whole-cell configuration). The increased secretion of GSH observed in the presence of S-CMC-Lys or 8-bromoadenosine-3',5'-cyclic monophosphate was also confirmed by HPLC assay of GSH on a confluent monolayer of respiratory cells. Western blot analysis confirmed the presence of CFTR in WI-26VA4 cells. This study suggests that S-CMC-Lys is able to stimulate a channel-mediated GSH secretion by human respiratory cells: electrophysiological and pharmacological characteristics of this channel are similar to those of the CFTR channel.

PHENYLALANINE 4-MONOOXYGENASE AND THE S-OXIDATION OF S-CARBOXYMETHYL-L-CYSTEINE IN HepG2 CELLS

The role of phenylalanine 4-monooxygenase (PAH) in the S-oxidation of S-carboxymethyl-L-cysteine (SCMC) in the rat has now been well established in rat cytosolic fractions in vitro. However, the role of PAH in the S-oxidation of SCMC in human cytosolic fractions or hepatocytes has yet to be investigated. The aim of this investigation was to analyse the kinetic parameters of PAH oxidation of both L-phenylalanine (Phe) and SCMC in the human HepG2 cell line in order to investigate the use of these cells as a model for the cellular regulation of SCMC S-oxidation. The experimentally determined Km and V(max) were 7.14 +/- 0.32 mM and 0.85 +/- 0.32 nmole Tyr formed min(-1) x mg protein(-1) using Phe as substrate. For SCMC the values were 25.24 +/- 5.91 mM and 0.79 +/- 0.09 nmole SCMC (RIS) S-oxides formed min(-1) x mg protein(-1). The experimentally determined Km and V(max) for the cofactor BH4 were 6.81 +/- 0.21 microM and 0.41 +/- 0.004 nmole Tyr formed min(-1) x mg protein(-1) for Phe and 7.24 +/- 0.19 microM and 0.42 +/- 0.002 nmole SCMC (R/S) S-oxides formed min(-1) x mg protein(-1) for SCMC. The use of various PAH inhibitors confirmed that HepG2 cells contained PAH and that the enzyme was capable of converting SCMC to its (R) and (S) S-oxide metabolites in an in vitro PAH assay. Thus HepG2 cells have become a useful additional tool for the investigation of the cellular regulation of PAH in the S-oxidation of SCMC.