X-Linked Myotubular Myopathy and Mitochondrial Function in Muscle and Liver Samples.

X-linked myotubular myopathy (XLMTM) is a rare congenital myopathy that commonly manifests with liver involvement. In most XLMTM cases, disease-causing variants have been identified in the myotubularin gene (MTM1) on chromosome Xq28, which encodes myotubularin protein (MTM1). The impairment of mitochondrial respiratory chain (MRC) enzyme activity in muscle has been observed in the XLMTM mouse model. Though several reports mentioned possible mechanisms of liver involvement in XLMTM patients and animal models, the precise underlying mechanisms remain unknown, and there is no report focused on mitochondrial functions in hepatocytes in XLMTM. We encountered two patients with XLMTM who had liver involvement. We measured MRC enzyme activities in two muscle biopsy specimens, and one liver specimen from our patients to investigate whether MTM1 variants cause MRC dysfunction and whether mitochondrial disturbance is associated with organ dysfunction. MRC enzyme activities decreased in skeletal muscles but were normal in the liver. In our patients, the impaired MRC enzyme activity found in muscle is consistent with previously reported mechanisms that the loss of MTM1-desmin intermediate filament and MTM1-IMMT (a mitochondrial membrane protein) interaction led to the mitochondrial dysfunction. However, our study showed that liver involvement in XLMTM may not be associated with mitochondrial dysfunction.

Advantage of a higher position of the tracheostoma with glottic closure for preventing complications related to tracheostomy tube: a retrospective cohort study.

BACKGROUND: Surgery to prevent aspiration has complications related to tracheostomy tube, such as the trachea-brachiocephalic artery fistula. Glottic closure procedure makes tracheostoma at a position higher than the first ring of the trachea and theoretically has a potential to prevent such complications owing to a longer distance between the tip of tracheostomy tube and the tracheal membrane adjacent to the brachiocephalic artery. Our aim is to evaluate the safety of glottic closure in neurologically impaired patients by comparing outcomes with laryngotracheal separation. METHODS: This study is a single-center retrospective study from 2004 to 2019, using data of 15 and 12 patients who underwent glottic closure (GC) and laryngotracheal separation (LTS). The primary outcome was the incidence of postoperative complications induced by tracheostomy tube placement and adjustment of the tracheostomy tube position to prevent these complications, such as by converting to a length-adjustable tube and/or placing gauze between the skin and tube flange. Additionally, we analyzed the anatomical relationship between the tracheostomy tube tip and brachiocephalic artery and measured the distance between them using postoperative CT images. RESULTS: No patients in either group had trachea-brachiocephalic artery fistula. Erosion or granuloma formation occurred in 1 patient (7%) and 4 patients (33%) in the GC and LTS groups, respectively. Adjustment of the tracheostomy tube was needed in 2 patients (13%) and 6 patients (50%) in the GC and LTS groups. CT revealed a higher proportion of patients with the tracheostomy tube tip superior to the brachiocephalic artery in GC than LTS group. The mean tracheostoma-brachiocephalic artery distance was 40.8 and 32.4 mm in the GC and LTS groups. CONCLUSIONS: Glottic closure reduces the risk of postoperative complications related to a tracheostomy tube. This may be due to the higher position of the tracheostoma at the level of the cricoid cartilage, increasing the distance between the tracheostoma and brachiocephalic artery.

Dexmedetomidine Exerts a Negative Chronotropic Action on Sinoatrial Node Cells Through the Activation of Imidazoline Receptors.

ABSTRACT: Dexmedetomidine (DEX), an α2-adrenoreceptor (α2-AR) and imidazoline receptor agonist, is most often used for the sedation of patients in the intensive care unit. Its administration is associated with an increased incidence of bradycardia; however, the precise mechanism of DEX-induced bradycardia has yet to be fully elucidated. This study was undertaken to examine whether DEX modifies pacemaker activity and the underlying ionic channel function through α2-AR and imidazoline receptors. The whole-cell patch-clamp techniques were used to record action potentials and related ionic currents of sinoatrial node cells in guinea pigs. DEX (≥10 nM) reduced sinoatrial node automaticity and the diastolic depolarization rate. DEX reduced the amplitude of hyperpolarization-activated cation current (If or Ih) the pacemaker current, even within the physiological pacemaker potential range. DEX slowed the If current activation kinetics and caused a significant shift in the voltage dependence of channel activation to negative potentials. In addition, efaroxan, an α2-AR and imidazoline I1 receptor antagonist, attenuated the inhibitory effects of DEX on sinoatrial node automaticity and If current activity, whereas yohimbine, an α2-AR-selective antagonist, did not. DEX did not affect the current activities of other channels, including rapidly and slowly activating delayed rectifier K+ currents (IKr and IKs), L-type Ca2+ current (ICa,L), Na+/Ca2+ exchange current (INCX), and muscarinic K+ current (IK,ACh). Our results indicate that DEX, at clinically relevant concentrations, induced a negative chronotropic effect on the sinoatrial node function through the downregulation of If current through an imidazoline I1 receptor other than the α2-AR in the clinical setting.

Questionnaire survey on mumps vaccination for parents in Nara prefecture, Japan.

BACKGROUND: Although the mumps vaccine has not been included in the national immunization program (NIP) in Japan, it has been shown that a two-dose routine vaccine program would be highly cost-effective. In this study, we carried outa questionnaire-based study to investigate how many Japanese parents want the mumps vaccine to be included in the NIP with proper information. METHODS: The questionnaire was given to parents who visited the Pediatrics or neonatal intensive care unit of Nara Prefecture General Medical Center, Nara City, Japan, between 1 March 2017 and 31 August 2017. The questionnaire consisted of information about mumps and six questions, for example (i) do parents know that mumps can be prevented by vaccine; (ii) do they know that they need to pay for mumps vaccines; and (iii) do they hope that the government will resume routine mumps vaccination. RESULTS: In total, 1,224 parents answered the questionnaire. A total of 81% and 75.4% of parents knew that mumps can be prevented by vaccination and that mumps vaccine is not included in the NIP, respectively, before reading the information. After reading the information, 95.0% of parents thought that mumps vaccine should be included in the NIP. While 61.7% of parents answered that they would choose two-dose vaccination without governmental financial support, 92.1% of them would choose two-dose vaccination with governmental financial support (P < 0.0001). CONCLUSION: Japanese parents want the mumps vaccine to be included in the NIP. Japan is able to start routine use of the mumps vaccine now.

[Anesthetic Induction in a Patient with Giant Ovarian Tumor Who Developed Severe Hemodynamic Instability].

A 45 year-old woman underwent a laparotomy for a giant ovarian tumor under general anesthesia. Preoperative CT scan revealed a 30 cm-diameter tumor compressing IVC. She had slight respiratory discomfort on supine position, but respiratory function test showed no abnormalities. In the operating room, after oxygenation for 3 minutes, general anesthesia was induced with fentanyl 100 µg, propofol 90 mg and rocuronium 40 mg on supine position. Immediately after the induction, her systolic blood pressure and heart rate fell to 45 mmHg and 40 beats per minute, respectively. We considered that her hemodynamic instability was supine hypotensive syndrome due to giant ovarian tumor. Therefore we placed her 30 degree right side up and pushed her tumor to the left so as not to compress the IVC. We rapidly injected acetated Ringer's solution 500 ml, ephedrine 12 mg and phenylephrine 0.1 mg, and her hemodynamic status soon recovered to normal ranges. The anesthetic induction of a patient with a giant ovarian tumor is challenging. Some reports recommend strategies such as induction on lateral position or suctioning tumor contents before induction. Careful induction of general anesthesia is required for these patients.

Estimation of relationship between the structure of 1,2,3,4-tetrahydroisoquinoline derivatives determined by a semiempirical molecular-orbital method and their cytotoxicity.

A semiempirical molecular-orbital method (CAChe 4.9, PM5) was applied to delineate the relationship between the cytotoxicity (evaluated by 50% cytotoxic concentration, CC(50)) of nineteen 1,2,3,4-tetrahydroisoquinoline derivatives, their molecular weight and the sixteen chemical parameters (descriptors) determined by CONFLEX/PM5 method. There was little or no correlation between the CC(50) in HL-60 cells and the heat of formation, stability of hydration (DeltaH), dipole moment, electron affinity, ionization potential, highest occupied molecular orbital energy (E(HOMO)), lowest unoccupied molecular orbital energy (E(LUMO)), absolute hardness (eta, softness and hardness of the molecule) or molecular weight (r(2)<0.312). On the other hand, there was a good correlation between the CC(50) and the hydrophobicity (log P) (r(2)=0.503), and the descriptors for the molecular size such as surface area (r(2)=0.771), volume (r(2)=0.805) and width (r(2)=0.757). Similar, but not so clear-cut correlation was found in HSC-2, HSC-3 and HSC-4 human oral squamous cell carcinoma cell lines. The present study demonstrates that the cytotoxicity of 1,2,3,4-tetrahydroisoquinoline derivatives depends more on the descriptors for molecular size rather than the physicochemical descriptors.

A structure-activity relationship study on the mechanisms of methacrylate-induced toxicity using NMR chemical shift of beta-carbon, RP-HPLC log P and semiempirical molecular descriptor.

To clarify the mechanism of methacrylate-induced toxicity, a total of 24 acrylates, methacrylates, and dimethacrylates were chosen for a structure-activity relationship (SAR) study in terms of NMR chemical shifts, semiempirical molecular descriptors, and reverse phase (RP)-HPLC log P. Molecular descriptors as well as bulk, electronic, and energy descriptors were calculated using the PM3/CONFLEX method. A significant multiple linear regression equation for methacrylates in mice was denoted as log 1/LD50 (which was function [-(E(HOMO)+E(LUMO))/2, log P]). Besides, significant linear regression equations for methacrylates were denoted as log 1/ED50 in HeLa S3 and in HGF cells as function [E(HOMO) and/or log P]. Results showed that the 13C NMR chemical shift of beta-carbon for methacrylates was correlated with their E(HOMO). Findings of this study thus suggested that it might be possible to predict methacrylate-induced toxicity using physicochemical properties.

Quantitative structure-cytotoxicity relationship analysis of 3-formylchromone derivatives by a semiempirical molecular-orbital method with the concept of absolute hardness.

A semiempirical molecular-orbital method (CAChe) was applied to delineate the relationship between the cytotoxicity (evaluated by 50% cytotoxic concentration, CC50) of 11 3-formylchromone derivatives and 15 chemical parameters (descriptors). The most stable conformation of all these compounds was exhibited by the planar structure. Compounds [2], [3], [4] and [9] had additionally protruding branches from the coplanar. In HSG cells, the best correlation coefficient was observed between CC50 and stability of hydration (DeltaH), followed by electron affinity, lowest unoccupied molecular orbital energy (ELUMO), highest occupied molecular orbital energy (EHOMO), ionization potential, absolute electron negativity (chi) and reactivity index (omega). When the value for [1], which was off from the regression line, was omitted, higher correlation coefficients were obtained between CC50 and electron affinity, ELUMO, chi and omega. When CC50 value was plotted vs. log P, a parabolic curve was produced, under the condition that the data for [5] were omitted. In HL-60 cells, moderate correlation was found between CC50 and DeltaH, electron affinity, ELUMO, chi and omega. When the values for [1] and [6], which were off the regression line, were omitted, higher correlation coefficients were obtained between CC50 and these five descriptors. In HSC-3 cells, there was moderate correlation between CC50 and the dipole moment, but not with other descriptors. In HSC-2 and MT-4 cells, there was no clear-cut correlation between CC50 and any of these descriptors. The present study indicates the applicability of HSG cells in searching for more active 3-formylchromone derivatives, using QSAR with the concept of absolute hardness.

Quantitative structure-cytotoxicity relationship analysis of 5-trifluoromethyloxazole derivatives by a semiempirical molecular-orbital method with the concept of absolute hardness.

The most stable conformation of twelve 5-trifluoromethyloxazole derivatives was calculated by CONFLEX 5. The optimized structure was determined by CAChe Worksystem 4.9 PM3 method, in the presence (COSMO) or absence (non-COSMO) of water. Higher correlation coefficients for all descriptors were found under COSMO, as compared with non-COSMO conditions. Good correlation was found between the cytotoxicity of these compounds and the electron affinity, ionization potential, highest occupied molecular orbital energy (E(HOMO)), lowest unoccupied molecular orbital energy (E(LUMO)), absolute hardness (eta) and reactivity index (omega). On the other hand, there was generally no clear-cut correlation between CC50 and the heat of formation, stability of hydration, dipole moment, absolute electron negativity (chi), molecular weight, maximum length of molecule, with some exceptions. The cytotoxic activity of 5-trifluoromethyloxazole derivatives became maximum at log p = 4.6. The concept of absolute hardness is applicable in estimating the cytotoxicity of 5-trifluoromethyloxazoles, using an eta-chi activity diagram.

Tumor-specificity and type of cell death induced by vitamin K2 derivatives and prenylalcohols.

Fourteen vitamin K2 (menaquinone (MK)-n, n = 1-14) and ten prenylalcohol derivatives (n = 1-10) with different numbers (n) of isoprenyl groups in the side chains were investigated for their cytotoxicity against nine human tumor cell lines and three human normal oral cells. Among the vitamin K2 derivatives, MK-2 (n = 2) showed the greatest cytotoxicity, followed by MK-1 (n = 1) and MK-3 (n = 3). MK-1, MK-2 and MK-3 showed the highest tumor-specific index (TS= > 2.0, 2.0 and > 1.7, respectively). Among the prenylalcohols, geranylgeraniol (GG) (n = 4) showed the highest cytotoxicity, followed by farnesol (n = 3) and geranylfarnesol (GF) (n = 3). GG showed the highest tumor-specificity (TS = 1.8), followed by farnesol (TS = > 1.4), GF (TS= > < 1.3). However, the tumor-specificity of MK-2 and GG was much lower than that of conventional chemotherapeutic agents. The human leukemic cell lines were the most sensitive, whereas the human glioblastoma cell lines were the most resistant to MK-2 and GG. MK-2 did not induce internucleosomal DNA fragmentation in either the human promyelocytic leukemia HL-60 or the human squamous cell carcinoma HSC-4 cell lines. GG induced marginal internucleosomal DNA fragmentation in the HL-60 cells, but not in the HSC-4 cells. Both MK-2 and GG did not induce the formation of autophagosomes, nor did they clearly change the intracellular concentration of three polyamines. Electron spin resonance (ESR) spectroscopy showed that only MK-1 (n = 1), as well as GGF (n = 7) and GFF (n = 8) which had lower cytotoxicity, produced radicals, suggesting the lack of connection between cytotoxicity and radical production. The present study demonstrates that the presence of 1,4-naphtoquinone structure (including alpha,beta-unsaturated ketones) in vitamin K2 derivatives confers on them the ability to induce non-apoptotic cell death.

Tumor-specific cytotoxicity and type of cell death induced by beta-cyclodextrin benzaldehyde inclusion compound.

The cytotoxicity of beta-cyclodextrin benzaldehyde inclusion compound (CDBA) against human normal and cancer cell lines was investigated. CDBA showed slightly higher cytotoxicity against human tumor cell lines, as compared to normal cells, with a tumor-specificity index of 2.2. Human myelogenous leukemia cell lines (HL-60, ML-1, KG-1) were the most sensitive to CDBA, followed by human oral squamous cell carcinoma (HSC-2, HSC-3, HSC-4) and human glioblastoma (T98G, U87MG). Human normal cells (gingival fibroblasts, pulp cells, periodontal ligament fibroblasts) were the most resistant. CDBA induced internucleosomal DNA fragmentation in HL-60 cells and caspase-3, -8, -9 activation, but to a much lesser extent than that attained by UV irradiation or actinomycin D. On the other hand, CDBA did not induce DNA fragmentation, nor caspase activation in HSC-2, HSC-4 or T98G cells. Electron microscopy demonstrated that CDBA induced the destruction of mitochondrial structure and digestion of broken organelles by secondary lysosomes in all of these cells. CDBA also increased the number of acidic organelles as judged by acridine orange staining. The present study suggests that CDBA induces autophagic cell death in cancer cell lines.

Tumor-specific cytotoxicity and type of cell death induced by peplomycin in oral squamous cell carcinoma cell lines.

The antitumor antibiotic peplomycin showed higher cytostatic antiproliferative effect on five cultured human oral squamous cell carcinoma (OSCC) cell lines (HSC-2, HSC-3, HSC-4, Ca9-22 and NA), as compared with three human oral normal cells (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF). Although the antiproliferative activity of peplomycin declined with increasing cell density, peplomycin showed tumor-specific cytotoxicity at any cell density. The five OSCC cell lines showed considerable differences in sensitivity against peplomycin; the HSC-2 cells were the most sensitive, followed by the NA, HSC-3, Ca9-22 and HSC-4 cells. Peplomycin did not induce internucleosomal DNA fragmentation in any of the five OSCC cell lines, and only slightly modified caspase-3, -8 and -9 activities in the HSC-2, Ca9-22 and NA cell lines. Electron microscopy revealed that peplomycin induced the vacuolation of mitochondria accompanying electron lucent matrices lacking cristae and the enlargement of the endoplasmic reticulum in the HSC-2 cells. These data suggest that the anti-proliferative effect of peplomycin is time-dependent, and therefore prolonged treatment with peplomycin in combination with cytotoxic chemotherapeutic agents may induce greater cytotoxic action.

Quantum-chemical descriptors for estimating hemolytic activity of aliphatic and aromatic methacrylates.

Methacrylates such as methyl methacrylate (6), triethyleneglycol dimethacrylate (5) and bisphenol A glycidyldimethacrylate, bis-GMA, (8) are widely used as materials in dental resins perturbation of the phosphatidylcholine-cholesterol interaction. Such effects of aromatic methacrylates may be involved in their marked hemolytic action.

QSAR of molecular structure and cytotoxic activity of vitamin K2 derivatives with concept of absolute hardness.

The correlation between the cytotoxicity of seven vitamin K2 (menaquinone) derivatives and thirteen chemical descriptors determined by CONFLEX5/CAChe Worksystem 4.9 (PM3) was investigated. After determination of the conformation of the seven vitamin K2 derivatives and approximation to the molecular form present in vivo (biomimetic) by CONFLEX5, the most stable structure was then determined by CAChe Worksystem 4.9 MOPAC (PM3). The vitamin K2 derivatives with one to three isoprenyl units [1-3] showed an extended form, whereas those with four to seven isoprenyl units [4-7] displayed a spherical form. The human hepatocellular carcinoma HepG2 cells displayed a good correlation between cytotoxicity and all the descriptors except for the electron affinity and lowest unoccupied molecular orbital energy (E(LUMO)). The absolute hardness (eta)--absolute electron negativity (chi) activity diagram determined by this calculation method may be useful for estimating the cytotoxic activity of vitamin K2 derivatives against HepG2 cells. The human squamous cell carcinoma HSC-2 and HSC-3 cells showed similar correlation. The human promyleocytic leukemia HL-60 cells showed the good correlation between cytotoxicity and molecular length. The present study demonstrates for the first time the best correlation between cytotoxic activity and molecular shape or molecular weight of vitamin K2 derivatives, regardless of the type of target cells.

Quantitative structure-activity relationship analysis of 4-trifluoromethylimidazole derivatives with the concept of absolute hardness.

A semiempirical molecular-orbital method (CAChe) was applied to delineate the relationship between the cytotoxicity (evaluated by 50% cytotoxic concentration, CC50) of thirteen 4-trifluoromethylimidazole derivatives and thirteen chemical descriptors derived by the CONFLEX/PM3 method. There was a highly significant relationship between CC50 and absolute electron negativity (chi). When the CC50 was plotted vs. the octanol-water distribution coefficient (log-P), a parabolic curve was produced, with a maximum cytotoxicity (or the least CC50 value) at log-P of 4.4. On the other hand, there was no significant relationship between CC50 and heat of formation, stability of hydration, dipole moment, ionization potential, energy of highest occupied moleculer orbital (E(HOMO)), molecular weight, or absolute hardness (eta). The present study demonstrates that the biological activity of 4-trifluoromethylimidazole derivatives can be estimated by an eta-chi activity diagram.

Quantitative structure-cytotoxicity relationship analysis of phenoxazine derivatives by semiempirical molecular-orbital method.

A semiempirical molecular-orbital method (CAChe) was applied to delineate the relationship between the cytotoxicity (evaluated by 50% cytotoxic concentration, CC50) of fifteen phenoxazine derivatives and eleven physical parameters (descriptors). Most of the phenoxazine derivatives had extended and planar structure. The cytotoxic activity of phenoxazines against the human oral squamous cell carcinoma HSC-2 and HSC-4 cells correlated to electron affinity, absolute hardness (eta), absolute electron negativity (chi) and octanol-water distribution coefficient (log-P). However, only log-P was correlated to CC50 in the HSC-3 cells, whereas only heat of formation and log-P were correlated to CC50 in the human promyelocytic leukemia HL-60 cells. The cytotoxic activity of the phenoxazine derivatives became maximum at the log-P = 5.9. Their cytotoxicity strongly depended on the chi value, but not on the eta value. Compounds with relatively higher cytotoxicity showed higher chi value (chi > 5.28), whereas compounds with relatively lower cytotoxicity showed lower chi value (chi < 4.27). These data suggest that appropriate chemical descriptors should be selected to estimate the cytotoxicity of phenoxazines, depending on the target cells.

Tumor-specificity and type of cell death induced by phenoxazines.

Phenoxazines have shown diverse biological activities, but tumor-specific cytotoxic activity has not been investigated. A total of 24 phenoxazine derivatives (WM1-24) was investigated for their relative cytotoxicity against human tumor cell lines vs. normal cells. WM7 and WM8 showed the highest tumor-specificity index of 4.3 and 4.8, respectively. Considerable difference in drug-sensitivity was found among these tumor cell lines. Human promyelocytic leukemia HL-60 cells showed the highest sensitivity to both WM7 and WM8, followed by human oral squamous cell carcinoma (HSC-2, HSC-3, HSC-4), and human gingival fibroblast (HGF), pulp cell (HPC) and periodontal ligament fibroblast (HPLF) were the most resistant. WM7 and WM8 induced little or no internucleosomal DNA fragmentation, and activated caspase-3 in HSC-2, HSC-4 and human glioblastoma T98G cells. These compounds failed to induce autophagic cell death, as judged by acridine orange and microtubule-associated protein 1 light chain 3 (LC3)-GFP assays. These results suggested that the higher cytotoxicity of WM7 and WM8 are derived from the positively-charged quaternary nitrogen substituents on the phenoxazine ring and the electron density of nitrogen at N12, and that inhibition of autophagy is not always coupled with apoptosis induction.

Tumor-specific cytotoxic activity and type of cell death induced by 4-trifluoromethylimidazoles in human oral squamous cell carcinoma cell lines.

Fourteen 4-trifluoromethylimidazole derivatives were investigated for their cytotoxicity against three human normal cells (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF) and four human tumor cell lines (oral squamous cell carcinoma HSC-2, HSC-3, HSC-4 and promyelocytic leukemia HL-60). Among these compounds, 4-trifluoromethyl-1,2-diphenylimidazole (IM5), 1-benzyl-4-trifluoromethyl-2-phenylimidazole (IM7) and 5-[1-ethoxy-2,2,2-trifluoro-1-(trifluoromethyl) ethyl]-1-methyl-2-phenyl-1H-imidazole (IM12) showed much higher cytotoxicity and tumor-specificity than the other compounds. IM5, the most potent compound, induced different types of cell death depending on the target cells. IM5 induced DNA fragmentation of oligonucleosomal units (a biochemical hallmark of apoptosis) in the HL-60 cells, but not in such a clear-cut laddering pattern in the HSC-2 cells. On the other hand, IM5 produced secondary lysosomes digesting broken organelles, without induction of internucleosomal DNA fragmentation and disappearance of cell surface microvilli in the HSC-4 cells, even though the HSC-2 and HSC-4 cells showed comparable sensitivity to IM5. These data suggest that the type of cell death is determined by the type of target cells, but not by the drug-sensitivity of the cells.

Review. Photooxygenation, photodegradation and antioxidative activity of platonin, a cyanine photosensitizing dye.

Platonin (4,4'-dimethyl-3,3'-di-n-heptyl-8-[2-(4methyl-3-n-heptylthiazole)] -2,2'-dicarbocyanine diiodine) is one of the photosensitive trithiazolepentamethine cyanine dyes. Visible light (VL)-promoted photodegradation products of platonin in an aqueous environment were identified as 3-heptyl4-methylthiazoline-2 -carbaldehyde (1), tetradecane-7-thiol (2), 1-nonene (3), heptylamine (4), 3-heptyl-4-methyl-2-thiazolone (5), 3-heptyl-4-methyl-2-thiothiazolone (6), 5-[2-(3-heptyl-4-methylthiazolidene)]-2-penten-l-aldehyde (7), gamma-(3-heptyl-4-methyl-2-thiazolidene)crotonic acid (8) and 3,5-di (4-methyl-2-thiazolyl)-2,4-pentadienic acid (9). The quantum yield of singlet oxygen (1O2 (1deltag)) derived from VL-promoted platonin formed heptyl and heptyl cation radicals together with the photodegradation products described above. In isolated rat hepatocytes, platonin was cytotoxic under VL irradiation, whereas non-irradiated platonin was less cytotoxic and improved cell viability. The effects of oxygen uptake and cell viability of photolysis photoproducts of platonin, 3-heptyl-2,4-dimethylthiazolium iodide (HDT) and 3-heptyl-4-methylthiazolium iodide (HMT) were compared with those of platonin. These compounds, particularly the former, showed greater cytotoxicity and brought about less oxygen uptake than the latter. Radical-scavenging activities of platonin using an induction period method demonstrated that fully oxidized platonin had a stoichiometric factor (n) of 4. Platonin was a potent peroxy-radical scavenger. The dual modulation activity of platonin as a prooxidant and an antioxidant under VL irradiation was revealed by monitoring the oxygen uptake in isolated rat hepatocytes. This antioxidant/prooxidant activity of platonin may induce diverse effective pharmacological activities in biological systems. In the light of recent developments in studies of platonin and related compounds, the VL-promoted photooxygenation, photodegradation, antioxidant activity and biological activity of platonin are discussed.