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Biomedical subjects

Mei Zhang

Publications and source records attributed to Mei Zhang.

At least 73 records · Page 4Linked to original sources

Strong, transparent, multifunctional, carbon nanotube sheets.

Individual carbon nanotubes are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. We demonstrated such assembly at rates above 7 meters per minute by cooperatively rotating carbon nanotubes in vertically oriented nanotube arrays (forests) and made 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of sheets of high-strength steel. These nanotube sheets have been used in laboratory demonstrations for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes.

Journal Article↗

Transcriptional profiling in mouse skeletal muscle following a single bout of voluntary running: evidence of increased cell proliferation.

Skeletal muscle undergoes adaptation following repetitive bouts of exercise. We hypothesize that transcriptional reprogramming and cellular remodeling start in the early phase of long-term training and play an important role in skeletal muscle adaptation. The aim of this study was to define the global mRNA expression in mouse plantaris muscle during (run for 3 and 12 h) and after (3, 6, 12, and 24 h postexercise) a single bout of voluntary running and compare it with that after long-term training (4 wk of running). Among 15,832 gene elements surveyed in a high-density cDNA microarray analysis, 900 showed more than twofold changes at one or more time points. K-means clustering and cumulative hypergeometric probability distribution analyses revealed a significant enrichment of genes involved in defense, cell cycle, cell adhesion and motility, signal transduction, and apoptosis, with induced expression patterns sharing similar patterns with that of peroxisome proliferator activator receptor-gamma coactivator-1alpha and vascular endothelial growth factor A. We focused on the finding of a delayed (at 24 h postexercise) induction of mRNA expression of cell cycle genes origin recognition complex 1, cyclin A2, and cell division 2 homolog A (Schizoccharomyces pombe) and confirmed increased cell proliferation by in vivo 5-bromo-2'-deoxyuridine labeling following voluntary running. X-ray irradiation of the hindlimb significantly diminished exercise-induced 5-bromo-2'-deoxyuridine incorporation. These findings suggest that a single bout of voluntary running activates the transcriptional network and promotes adaptive processes in skeletal muscle, including cell proliferation.

Animals↗

Cloning and functional characterization of NtCPK4, a new tobacco calcium-dependent protein kinase.

A cDNA clone, encoding calcium (Ca2+)-dependent protein kinase (CDPK or CPK), was isolated from tobacco (Nicotiana tabacum). The full-length cDNA of 2360 bp contains an open reading frame for NtCPK4 consisting of 572 amino acid residues. Sequence alignment indicated that NtCPK4 shared high similarities with other CPKs and some CPK-related protein kinases (CRKs). Biochemical analyses showed that NtCPK4 phosphorylated itself and calf thymus histones fraction III-S (histone III-S) in a calcium-dependent manner, and the K0.5 of calcium activation was 0.29 microM or 0.25 microM with histone III-S or syntide-2 as substrates, respectively. The Vmax and Km were 588 nmol min-1 mg-1 and 176 microg ml-1, respectively, when histone III-S was used as substrate, while they were 2415 nmol min-1 mg-1 and 58 microM, respectively, with syntide-2 as substrate. In addition, the phosphorylation of NtCPK4 occurred on threonine residue, as shown by capillary electrophoresis analyses. All of these data demonstrated that NtCPK4 was a serine/threonine protein kinase. NtCPK4 as a low copy gene was expressed in all tested organs including the root, leaf, stem, and flower of tobacco, while its expression was temporally and spatially modulated in both productive and vegetative tissues during tobacco growth and development. NtCPK4 expression was also increased in response to the treatment of gibberellin or NaCl. Our study suggested that NtCPK4 might play vital roles in plant development and responses to environmental stimuli.

Amino Acid Sequence↗

Cardiolipin is essential for organization of complexes III and IV into a supercomplex in intact yeast mitochondria.

Digitonin extracts of mitochondria from cardiolipin-containing (wild type) and cardiolipin-lacking (crd1Delta mutant) Saccharomyces cerevisiae subjected to colorless native polyacrylamide gel electrophoresis in the presence of 0.003% digitonin displayed a supercomplex composed of homodimers of complexes III and IV in the former case but only the individual homodimers in the latter case. To avoid treatment with any detergent or dye, we compared organization of the respiratory chain in intact mitochondria from wild type and cardiolipin-lacking cells by using a functional analysis developed previously for the study of the organization of the respiratory chain of S. cerevisiae (Boumans, H., Grivell, L. A., and Berden, J. A. (1998) J. Biol. Chem. 273, 4872-4877). Dependence of the kinetics of NADH oxidation via complexes III, IV, and cytochrome c on the concentration of the complex III-specific inhibitor antimycin A was studied. A linear relationship between respiratory activity and saturation of complex III with antimycin A was obtained for wild type mitochondria consistent with single functional unit kinetics of the respiratory chain. Under the same conditions, cardiolipin-lacking mitochondria displayed a hyperbolic relationship indicating cytochrome c pool behavior. No release of cytochrome c from cardiolipin-lacking mitochondria or mitoplasts under our standard experimental conditions was detected. Identical cytochrome c pool behavior was observed for both wild type and cardiolipin-lacking mitochondria in the presence of a chaotropic agent, which disrupts the interaction between respiratory complexes. The results demonstrate that cardiolipin is essential for association of complexes III and IV into a supercomplex in intact yeast mitochondria.

Antimycin A↗

Transfer of rofecoxib into human milk.

OBJECTIVE: To determine the milk-to-plasma (M/P) concentration ratio of rofecoxib in lactating mothers and estimate likely infant exposure. METHODS: Rofecoxib 25 mg was given to six lactating women at weaning. Blood and milk were sampled up to 72 h post-dose for determination of rofecoxib concentrations. M/P ratios were derived from the respective area under the concentration-time curves. The infant 'dose' in milk was estimated and expressed as a percentage of the maternal dose, corrected for weight. RESULTS: The median (range) M/P ratio and infant 'dose' were 0.25 (0.16-0.32) and 2.1% (1.8-3.2%), respectively. CONCLUSIONS: The use of rofecoxib during breastfeeding is unlikely to pose harm to the suckling infant on the basis of low transfer into human milk.

Adult↗

Exercise stimulates Pgc-1alpha transcription in skeletal muscle through activation of the p38 MAPK pathway.

Peroxisome proliferator-activated receptor gamma co-activator 1alpha (PGC-1alpha) promotes mitochondrial biogenesis and slow fiber formation in skeletal muscle. We hypothesized that activation of the p38 mitogen-activated protein kinase (MAPK) pathway in response to increased muscle activity stimulated Pgc-1alpha gene transcription as part of the mechanisms for skeletal muscle adaptation. Here we report that a single bout of voluntary running induced a transient increase of Pgc-1alpha mRNA expression in mouse plantaris muscle, concurrent with an activation of the p38 MAPK pathway. Activation of the p38 MAPK pathway in cultured C2C12 myocytes stimulated Pgc-1alpha promoter activity, which could be blocked by the specific inhibitors of p38, SB203580 and SB202190, or a dominant negative p38. Furthermore, the p38-mediated increase in Pgc-1alpha promoter activity was enhanced by increased expression of the downstream transcription factor ATF2 and completely blocked by ATF2DeltaN, a dominant negative ATF2. Skeletal muscle-specific expression of a constitutively active activator of p38, MKK6E, in transgenic mice resulted in enhanced Pgc-1alpha and cytochrome oxidase IV protein expression in fast-twitch skeletal muscles. These findings suggest that contractile activity-induced activation of the p38 MAPK pathway promotes Pgc-1alpha gene expression and skeletal muscle adaptation.

Activating Transcription Factor 2↗

The stomatin/prohibitin/flotillin/HflK/C domain of flotillin-1 contains distinct sequences that direct plasma membrane localization and protein interactions in 3T3-L1 adipocytes.

Flotillin-1 is a lipid raft-associated protein that has been implicated in various cellular processes. We examined the subcellular distribution of flotillin-1 in different cell types and found that localization is cell type-specific. Flotillin-1 relocates from a cytoplasmic compartment to the plasma membrane upon the differentiation of 3T3-L1 adipocytes. To delineate the structural determinants necessary for its localization, we generated a series of truncation mutants of flotillin-1. Wild type flotillin-1 has two putative hydrophobic domains and is localized to lipid raft microdomains at the plasma membrane. Flotillin-1 fragments lacking the N-terminal hydrophobic stretch are excluded from the lipid raft compartments but remain at the plasma membrane. On the other hand, mutants with the second hydrophobic region deleted fail to traffic to the plasma membrane but are instead found in intracellular granule-like structures. Flotillin-1 specifically interacts with the adaptor protein CAP, the Src family kinase Fyn, and cortical F-actin in lipid raft microdomains in adipocytes. Furthermore, CAP and Fyn associate with different regions in the N-terminal sequences of flotillin-1. These results furthered our understanding for how flotillin-1 can function as a molecular link between lipid rafts of the plasma membrane and a multimeric signaling complex at the actin cytoskeleton.

Adipocytes↗

Effect of resveratrol on microcirculation disorder and lung injury following severe acute pancreatitis in rats.

AIM: To investigate the mechanism of resveratrol underlying the microcirculation disorder and lung injury following severe acute pancreatitis (SAP). METHODS: Twenty-four rats were divided into 3 groups (SAP, sham and resveratrol groups) randomly. SAP model was established by injecting 4% sodium taurocholate 1 mL/kg through puncturing pancreatic ducts. Sham (control) group (8 rats) was established by turning over the duodenum. Resveratrol was given at 0.1 mg/kg b.m. intraperitoneally. Rats were sacrificed 9 h after SAP was induced. Blood samples were obtained for hemorrheological examination. Lung tissues were used for pathological observation, and examination of microvascular permeability, dry/wet ratio and myeloperoxidase (MPO) activity. Gene expression of intercellular adhesion molecule-1 (ICAM-1) was detected by RT-PCR. RESULTS: Compared with SAP group, resveratrol relieved the edema and infiltration of leukocytes in the lungs. Resveratrol improved markers of hemorrheology: high VTB (5.77+/-1.18 mPas vs 9.49+/-1.34 mPas), low VTB (16.12+/-3.20 mPas vs 30.91+/-7.28 mPas), PV (4.69+/-1.68 mPas vs 8.00+/-1.34 mPas), BSR (1.25+/-0.42 mm/h vs 0.03+/-0.03 mm/h), VPC (54.67+/-3.08% vs 62.17+/-3.39%), fibrinogen (203.2+/-87.8 g/ L vs 51.3+/-19.1 g/L), original hemolysis (0.45+/-0.02 vs 0.49+/-0.02), and complete hemolysis (0.41+/-0.02 vs 0.43+/-0.02) (P<0.05). Resveratrol decreased the OD ratio of ICAM-1 gene (0.800+/-0.03 vs 1.188+/-0.10), dry/wet ratio (0.74+/-0.02 vs 0.77+/-0.03), microvascular permeability (0.079+/-0.006 vs 0.112+/-0.004) and MPO activity (4.42+/-0.32 vs 5.03+/-0.51) significantly (P<0.05). CONCLUSION: Resveratrol can improve the microcirculation disorder of the lung by decreasing leukocyte-endothelial interaction, reducing blood viscosity, improving the decrease of blood flow, and stabilizing erythrocytes in SAP rats. It may be a potential candidate to treat SAP and its severe complications (ALI).

Acute Disease↗

Interleukin-1beta-induced transdifferentiation of renal proximal tubular cells is mediated by activation of JNK and p38 MAPK.

Interleukin (IL)-1beta induces renal tubular epithelial cells to transdifferentiate to myofibroblasts, which express alpha-smooth muscle actin (alpha-SMA). To understand the signal transduction mechanisms involved in transdifferentiation, we examined the roles of mitogen-activated protein kinases (MAPKs) in IL-1beta-stimulated alpha-SMA expression and cell migration in the HK-2 human renal proximal tubular cell line. IL-1beta induced the transdifferentiation of renal proximal tubular cells, which was characterized by upregulated expression of alpha-SMA and increased cell migration. In addition, IL-1beta increased the activity of the three members of the MAPK family, ERK, JNK and p38 MAPK, in these cells. Both SP600125, a specific inhibitor of JNK, and SB203580, a specific inhibitor of p38 MAPK, suppressed the IL-1beta-induced expression of alpha-SMA and cell migration, but these effects were not observed with PD98059, a specific inhibitor of ERK. These results suggest that IL-1beta-induced HK-2 cell transdifferentiation is mediated, at least in part, through the activation of the JNK and p38 MAPK signaling pathways.

Actins↗

Peripheral nerve regeneration.

The nerve chamber model has dominated the experimental study of peripheral nerve (PN) regeneration with animal models as well as in several clinical applications, such as the treatment of paralysis of limbs following severe trauma. The two stumps resulting from nerve transection are inserted inside a tubular chamber made from one of several materials, occasionally filled with various substances, and the quality of the reconnected nerve is assayed. Recent use of methods for data reduction has led to generation of a large normalized database from independent investigations. Methods for data normalization (reduction) are based on systematic use of the critical axon elongation, Lc, the gap length between the transected stumps at which the frequency of reconnection is just 50% for a given configuration. Four theories are compared for their ability to explain the normalized data. Although the neurotrophic and contact guidance theories explain some of the data, combined use of the more recent microtube theory and pressure cuff theory appears capable of explaining a much larger data set. PN regeneration appears to be upregulated by chamber configurations that facilitate formation of basement membrane microtubes about 10-20 microm in diameter, comprising linear columns of Schwann cells surrounded by basement membrane, into which axons elongate and eventually become myelinated. Regeneration is downregulated by experimental configurations that permit formation of a contractile cell (myofibroblast) capsule around the regenerating nerve that appears to restrict growth of a nerve trunk by application of circumferential mechanical forces. These two processes work competitively to regulate nerve regeneration in the chamber model.

Axons↗

Changes in integrin expression during adipocyte differentiation.

3T3-L1 preadipocytes require cAMP for maximal differentiation. Microarray analysis reveals that the integrins alpha5 and alpha6 are coordinately regulated by cAMP. alpha5 expression is gradually diminished during adipogenesis, whereas alpha6 is increased. Overexpression of alpha5 in preadipocytes results in enhanced proliferation and attenuated differentiation. Conversely, alpha6 overexpression is without effect. The GTPase Rac is normally inhibited during differentiation. However, overexpression of integrin alpha5 increases Rac activity. Constitutively active but not dominant-negative Rac inhibits differentiation when overexpressed in preadipocytes, implying its role downstream of alpha5 integrin in maintaining preadipocytes in an undifferentiated state. Moreover, alpha6 integrin is critically involved in clustering growth-arrested preadipocytes on basement membrane Matrigel. Perturbation of such clustering enhances Rho activity and promotes growth-arrested preadipocytes to reenter the cell cycle. These findings demonstrate a role for integrin alpha6 in connecting morphogenesis with signaling processes leading to terminal differentiation.

3T3-L1 Cells↗

Preoperative antibiotic and steroid therapy and hearing loss caused by semicircular canal transection in pseudomonas otitis media.

OBJECTIVE: The purpose of this experiment was to determine whether preoperative administration of antibiotics and corticosteroids can attenuate the severity of hearing loss (HL) with semicircular canal (SC) transection in a guinea pig model of Pseudomonas aeruginosa (PA) otitis media (OM). Study design and setting Prospective and controlled. METHODS: OM was induced in 64 pigmented guinea pigs by bilateral, transtympanic injection of PA. Two to 4 days later, 1 horizontal SC was randomly transected. In the 1st series, antibiotic therapy was initiated either immediately before or after surgery. In the 2nd series, all animals received preoperative antibiotics, and half received dexamethasone before surgery. Hearing was tested before and after surgery. RESULTS: PA was recovered in all ears. SC transection was associated with significant HL. HL was better in animals given antibiotics preoperatively (clicks, 16 versus 32 dB, P = 0.0220). Addition of preoperative steroids did not significantly further reduce HL (7 versus 14 dB for clicks, P = 0.6919). CONCLUSIONS: HL caused by SC transection in PA OM may be attenuated with preoperative antibiotic therapy in the guinea pig.

Animals↗

Hearing loss and extent of labyrinthine injury in Pseudomonas otitis media.

OBJECTIVES: To determine if the severity of hearing loss due to semicircular canal transection (SCT) in Pseudomonas otitis media (POM) is a function of the extent of the labyrinthine injury. METHODS: POM was induced bilaterally in 45 guinea pigs. After 2 to 4 days, SCT was performed in one 1 on the horizontal canal, the superior canal, or both the horizontal and the superior canals. Auditory-evoked brainstem responses were measured before and after SCT. RESULTS: POM was induced bilaterally in all animals. Elevation of click thresholds was found in almost all SCT ears of all 3 groups; however, there were no significant differences between groups. Comparing the SCT ear to the contralateral, control ear, mean hearing losses in the horizontal, superior, and horizontal + superior SCT groups were 23 dB, 27 dB, and 24 dB, respectively. CONCLUSIONS: Hearing loss does not correlate with extent of labyrinthine injury in POM in the guinea pig. EBM RATING: B-2.

Animals↗

Cellular localization and biochemical characterization of a novel calcium-dependent protein kinase from tobacco.

By screening tobacco cDNA library with MCK1 as a probe, we isolated a cDNA clone NtCPK5 (accession number AY971376), which encodes a typical calcium-dependent protein kinase. Sequence analyses indicated that NtCPK5 is related to both CPKs and CRKs superfamilies and has all of the three conserved domains of CPKs. The biochemical activity of NtCPK5 was calcium-dependent. NtCPK5 had Vmax and Km of 526 nmol/min/mg and 210 microg/ml respectively with calf thymus histone (fraction III, abbreviated to histone IIIs) as substrate. For substrate syntide-2, NtCPK5 showed a higher Vmax of 2008 nmol/min/mg and a lower Km of 30 microM. The K0.5 of calcium activation was 0.04 microM or 0.06 microM for histone IIIs or syntide-2 respectively. The putative myristoylation and palmitoylation consensus sequence of NtCPK5 suggests that it could be a membrane-anchoring protein. Indeed, our transient expression experiments with wild type and mutant forms of NtCPK5/GFP fusion proteins showed that NtCPK5 was localized to the plasma membrane of onion epidermal cells and that the localization required the N-terminal acylation sites of NtCPK5/GFP. Taking together, our data have demonstrated the biochemical characteristics of a novel protein NtCPK5 and its subcellular localization as a membrane-anchoring protein.

Amino Acid Sequence↗

Strategies of antigen-specific T-cell-based immunotherapy for cancer.

The critical role of antigen-specific T-cells in the eradication of cancer has been demonstrated in numerous animal models, while significant challenges need to be conquered before antigen-specific T-cell immunotherapy can achieve true success in clinical practice. These challenges include: (1) weak or nonimmunogenicity of spontaneous tumors, (2) negative immune regulation mechanisms of the host immune system, (3) immune inhibition exerted by tumor cells, (4) physical barrier in solid tumor, and (5) escape or resistance to immune attack by tumor cells. Nonetheless, significant success has been achieved in several clinical trials recently, highlighting the possibility of successful manipulation of the immune system for control and elimination of tumor. We focused our study on summarizing the current knowledge and corresponding strategies for improving autologous cytotoxic T-cell (CTL)-based cancer immunotherapy, which include the following aspects: (1) the selection of tumor antigens for stimulation of CTL, (2) strategies of enhancing maturation and antigen presentation activity of dendritic cells (DC), (3) strategies of activation and maintenance of CTL response, and (4) recruitment of suitable immune effector cells to tumor sites. The successful manipulation of the immune system, based on the more and more detailed knowledge of tumor immunology, may finally reach the goal of "immune surveillance of malignancy."

Animals↗

High rate of joint capsule matrix turnover in chronic human elbow contractures.

The joint capsule is a key component in posttraumatic joint contractures. The capsule is described as thickened, but little data exist supporting the observation. Our hypotheses were that mRNA levels of (1) collagen; (2) decorin and biglycan; (3) matrix metalloproteinases; and (4) tissue inhibitors of matrix metalloproteinases were significantly elevated in anterior joint capsules obtained from 11 patients having surgery for posttraumatic contractures when compared with nine elbows, from organ donors, that were free of contractures. Reverse transcription-polymerase chain reaction was used to evaluate mRNA expression normalized to a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase. In the joint capsules of the patients with elbow contractures, relative mRNA levels were increased for: collagen Types I, III, and V (1.5-2.5 times); biglycan (1.5 times); and matrix metalloproteinases-1, -2, -9, -13, and -15 (1.6-3.9 times). In contrast, expression of tissue inhibitors of matrix metalloproteinases-1, -2, and -4 were decreased (1/3-3/4 times) in the capsules of patients with contractures. There was no difference between the groups in relative mRNA expression for decorin, matrix metalloproteinases-8, -14 and -16, and tissue inhibitor of matrix metalloproteinase-3. The results indicate that joint capsule matrix molecule mRNA levels are altered in the chronic stages of posttraumatic elbow contractures in humans, potentially creating an environment with high matrix turnover rates.

Adolescent↗

Altered corneal nerves in aqueous tear deficiency viewed by in vivo confocal microscopy.

PURPOSE: To define the alterations of corneal nerves in aqueous tear deficiency dry eye patients with or without Sjögren syndrome and to identify the relationship between the morphologic changes of corneal nerves and the extent of dry eye. METHODS: Confocal microscopy was used to examine 38 consecutive aqueous tear deficiency patients (8 Sjögren syndrome and 30 non-Sjögren syndrome) and 30 age- and gender-matched normal controls. Images taken by Confocal2 slit-scanning microscope at subbasal epithelial cell layer of central cornea were analyzed. The number and density of corneal nerves and their size, beads, tortuosity, and branching pattern were compared. These data were correlated with age and the degree of dry eye. RESULTS: Sjögren syndrome patients showed a significant increase in average nerve number and tortuosity as compared with normal controls (P = 0.031 and 0.021, respectively). Severe nerve tortuosity (grade 4) and nerve branching appeared more frequently in aqueous tear deficiency than in normal subjects (P = 0.024 and 0.042, respectively). A decreased nerve number was observed with age in the normal controls (P = 0.002). However, such a correlation did not exist in aqueous tear deficiency. In aqueous tear deficiency, rose bengal staining score correlated positively with nerve density (P = 0.048) and nerve number (P = 0.001). Corneal fluorescein staining score was also positively correlated with nerve number (P = 0.027). CONCLUSIONS: Abnormal morphologic changes are observed in aqueous tear deficiency that are more severe in Sjögren syndrome. The distinct changes of corneal nerves include increased nerve number, tortuosity, and chances of branching, suggesting an attempted nerve regeneration. A strong correlation exists between the changes of nerve morphology and the degree of dry eye. These results provide some possible evidence for the abnormal corneal sensation in dry eye.

Adult↗

Plasminogen kringle 5 inhibits alkali-burn-induced corneal neovascularization.

PURPOSE: Plasminogen kringle 5 (K5) is a potent angiogenic inhibitor. The purpose of the present study was to evaluate the therapeutic effect of K5 on alkali-burn-induced corneal neovascularization (NV) and to investigate its mechanism of action. METHODS: Corneal NV was induced in rabbits by NaOH. The rabbits received eye drops containing K5 or vehicle alone, four times per day. Corneal NV and inflammation were monitored every other day with a slit lamp microscope, and the length of the vessels in the cornea and the area of NV were measured. Vascular endothelial growth factor (VEGF) was determined by immunohistochemical and Western blot analyses. The TUNEL assay was used to assess the apoptosis of endothelial cells. The effects of K5 on primary bovine aortic endothelial cells (BAECs) were determined by MTT assay, flow cytometry, transmission electron microscopy, and DNA fragmentation assay. RESULTS: Alkali-burn-induced progressive corneal NV and inflammation in the cornea. K5 delayed the onset of corneal NV (P < 0.05) and decreased NV areas (P < 0.05) in a dose-dependent manner. K5 treatment, after the formation of corneal NV, induced regression of newly formatted vessels in the cornea. K5 decreased the inflammatory index in the corneas at different time points after the alkali burn. Corneal VEGF levels were reduced by K5 treatment. K5 inhibits proliferation and induces apoptosis in BAECs. CONCLUSIONS: Topical application of K5 may have therapeutic potential for the chemical burn-induced corneal NV and inflammation. The inhibitory effect of K5 on corneal NV may be by downregulation of VEGF expression.

Administration, Topical↗