In Vitro Alternatives and Phototoxicity Testing. II. Effects of Reactive Oxygen Species in In Vitro Phototoxicity Assays

The effects of reactive oxygen species (including singlet oxygen) in two in vitro phototoxicity assays -- the 3T3 cell neutral red uptake phototoxicity (3T3 NRU PT) assay and the photohaemolysis assay -- were assessed by using scavengers. Fifteen test substances, which had previously been shown to be phototoxic in vitro, were assessed. Eleven of these produced singlet oxygen. The major factor in the photodynamic reaction of bithionol was thought to be a Type I reaction, because bithionol did not produce singlet oxygen and did not react to histidine. Acridine was regarded as a Type II substance, because of the evident effect of histidine as a scavenger. 8-Methoxypsoralen and 5-methoxypsoralen produced singlet oxygen, but their actions were not affected by the scavengers. In this study, we confirmed that reactive oxygen species have great effects in in vitro phototoxicity, and that the 3T3 NRU PT assay can be used to detect effects which are thought to be the direct reaction of an excited photosensitiser to biological substrates (Type III reaction), for example, 8-methoxypsoralen. Therefore, we suggest that photohaemolysis and phototoxicity could be used to evaluate the photodynamic mechanisms of photosensitising chemicals.

Simultaneous optimization of wet granulation process involving factor of drug content dependency on granule size

Computer optimization technique was applied to the simultaneous optimization of wet granulation process by a high-speed mixer granulator. Four pharmaceutical properties, including yield, drug content uniformity, geometrical mean diameter of granules, and uniformity of granule size, were selected to evaluate the quality of the granules. In particular, dependence of drug content uniformity on granule size was investigated using two model drugs, ascorbic acid and ethenzamide. An appreciable dependence of ascorbic acid content on granule size was not observed in model formulations. On the other hand, ethenzamide was contained more in small-size granules, and its content was decreased with an increase in amounts of hydroxypropyl cellulose (HPC-L; used as a binder) and binder solution. These observations suggested that drug content uniformity is influenced not only by drug solubility in the binder solution, but also by the use of HPC-L. A simultaneous optimal point incorporating four pharmaceutical properties was obtained using the generalized distance function. The experimental values of the four response variables obtained in newly prepared granules were found to correspond well with the predicted values of both granules containing ascorbic acid and ethenzamide. These results suggested that computer optimization would benefit the wet granulation process even if drug content segregation was involved in the process. Further, data obtained from computer optimization, in particular the contour diagram, will be valuable in the process validation.

In vitro degradation of tropoelastin by reactive oxygen species

The effects of reactive oxygen species (ROS) on elastin molecules (tropoelastin) were studied in vitro. ROS generated by ultraviolet A and hematoporphyrin rapidly degraded tropoelastin within 5 min. Their degradative activity was inhibited by the addition of NaN3. Treatment of tropoelastin with copper sulfate/ascorbic acid resulted in degradation of tropoelastin producing fragments of molecular weight 45, 30 and 10 kDa within 30 min. The degradation of tropoelastin was partially blocked by the addition of mannitol. ROS induced by the xanthine/xanthine oxidase system also degraded tropoelastin within 6 h. The degradation was blocked by catalase but not by superoxide dismutase (SOD). ROS generated by copper-ascorbate seems to be unique in that it cleaves relatively specific sites of the tropoelastin molecule. Thus ROS may play a degradative role in elastin metabolism which may cause the elastolytic changes or the deposition of fragmented elastic fibers in photoaged skin or age-related elastolytic disorders.

Optimization of the granulation process for designing tablets

A computer optimization technique based on surface response methodology was applied to optimize the wet granulation process for designing tablets. Physical properties (mean granule size, granule size distribution, compressibility, granule strength) of a model granule formulation containing ethenzamide were accurately described by a second polynomial equation based on two independent variables (amounts of binder and binder solution). This regression equation also gave a good correlation for three physical properties of tablets (distintegration time, compactibility, compression force variance), but the correlation for tablet hardness and weight variation was poor. These results imply that not only the above physical properties of granules but also the rheological behavior and porous structure of granules are closely related to tablet properties. Using an optimization of five tablet properties using the generalized distance function, the predicted values of the physical properties of both granules and tablets agreed well with experimental values. This agreement indicates that the computer optimization technique is useful for optimizing the granulation process for designing tablets.

Linoleic acid and alpha-linolenic acid lightens ultraviolet-induced hyperpigmentation of the skin

This study was conducted to evaluate the effects of unsaturated fatty acids on ultraviolet-induced hyperpigmentation of the skin. An efficient lightening effect was observed following topical application of linoleic acid or alpha-linolenic acid to UV-stimulated hyperpigmented dorsal skin of brownish guinea pigs. The number of melanocytes in the treated skin was similar to the number in the skin of the pigmented control, indicating that the pigment-lightening effect was not due to depletion of melanocytes. In vitro experiments using cultured murine melanoma cells showed that melanin production was inhibited most effectively by alpha-linolenic acid, followed by linoleic acid and then by oleic acid. Furthermore, the turnover of the stratum corneum, which plays an important role in the removal of melanin pigment from the epidermis, was accelerated by linoleic acid and by alpha-linolenic acid. Taken together, the results suggest that the pigment-lightening effects of linoleic acid and alpha-linolenic acid are, at least in part, due to suppression of melanin production by active melanocytes, and to enhanced desquamation of melanin pigment from the epidermis.

Prevention of hypoglycaemia in a patient with type Ib glycogen storage disease by an amylase (alpha-glucosidase) inhibitor

Patients with type Ib glycogen storage disease (GSD Ib) are susceptible to hypoglycaemic episodes. To determine whether an amylase (alpha-glucosidase) inhibitor, voglibose, can be useful in the control of hypoglycaemia, we tried it in a 14-y-old male with GSD Ib. Oral administration of voglibose prolonged the duration of normoglycaemia and reduced the incidence of hypoglycaemia attacks. These findings indicate that voglibose may be useful for preventing hypoglycaemia in GSD Ib patients.

Cross-linking of collagen by singlet oxygen generated with UV-A

Singlet oxygen (1O2), a highly reactive and toxic intermediate, may play a role in photo-induced aging. We examined singlet oxygen generation from hematoporphyrin (HP) with UV-A, by monitoring the emission at 1,268 nm corresponding to 1O2 --> 3O2. Singlet oxygen was formed HP-dose-dependently in this system. We then investigated the reaction of singlet oxygen generated by UV-A irradiation with collagen, which is related to skin elasticity and softness. Collagen from skin was rapidly and dose-dependently cross-linked by singlet oxygen. The reaction was inhibited by NaN3, a selective quencher of singlet oxygen. In contrast, SOD (superoxide dismutase) and mannitol had no effect. These results suggested that cross-linking of collagen was caused by UV-A-generated singlet oxygen, not by any other reactive oxygen species. Compared with another multisubunit protein, alcohol dehydrogenase, collagen was cross-linked much more efficiently. Further, the finding that semicarbazide inhibited cross-linking of collagen showed that cross-links were formed between photooxidized histidyl residues and amino groups. Singlet oxygen generated by UV-A irradiation may contribute to cross-linking of collagen in the process of skin photoaging.

Study of the effective dose of a topical antifungal agent, omoconazole nitrate, on the basis of percutaneous pharmacokinetics in guinea-pigs and mice

The clinically useful optimum dose of omoconazole nitrate, a topical antifungal agent, has been examined by analysing the percutaneous pharmacokinetics of the drug to assess its pharmacological activity in an in-vivo study. Creams containing omoconazole nitrate were prepared on a pilot basis. The therapeutic effect of the omoconazole nitrate creams was examined in an in-vivo pharmacological dermatophytosis infection model in guinea-pigs. Creams containing 0.25% or higher concentrations of omoconazole nitrate resulted in significant inhibition compared with no treatment and with vehicle-treated controls. In the mycological examination no growth of dermatophytes was observed for creams containing 1% or higher concentrations. In an in-vitro hairless mouse skin-permeability test a non-linear least squares program based on a fast inverse Laplace transform algorithm was used to calculate the partition and diffusion parameters of omoconazole nitrate in the stratum corneum and viable epidermis. The time-course of drug concentrations in the skin of the guinea-pig, estimated on the basis of these parameters, led to predictions that percutaneous drug concentrations on the guinea-pig would require 10 or more days to reach equilibrium in the skin; that drug concentrations in the corneum-viable epidermis border, where dermatophytes are considered to grow, would exceed the minimum effective concentration when 0.1% higher concentration creams were used; and that for binding to keratin drug concentrations would reach the practical minimum effective concentration when creams containing 0.5% or more omoconazole nitrate were used. These results show that partition and diffusion parameters obtained from in-vitro skin permeation studies can be used to predict in-vivo percutaneous pharmacokinetics and to estimate therapeutically effective concentrations.

Participation of reactive oxygen species in phototoxicity induced by quinolone antibacterial agents

To elucidate the mechanism of phototoxicity induced as a side effect by some of the new quinolone antibiotics, we studied sparfloxacin (SPFX), lomefloxacin, enoxacin, ofloxacin, and ciprofloxacin. We first examined the photosensitized formation of reactive oxygen species such as singlet oxygen (1O2) and superoxide anion (O2-) mediated by the new quinolones. Although a large number of studies have been reported, there is no direct evidence that these drugs generate reactive oxygen species. We employed a near-infrared emission spectrometer to detect 1O2-specific emission (1268 nm), and the nitroblue tetrazolium reduction method to detect O2-. All the quinolones investigated in this study were found to produce 1O2. Four drugs, but not SPFX, produced O2-. We also examined photodynamic DNA strand-breaking activity as a possible mechanism to explain the participation of reactive oxygen species in the phototoxicity of the drugs. All the drugs exhibited photodynamic DNA strand-breaking activity. The inhibitory effect of scavengers of reactive oxygen species indicated that the main active species was 1O2. The DNA strand-breaking activity was correlated not with the 1O2-forming ability, but with the affinity of the drugs for DNA. This result may be due to the short lifetime of 1O2. These data suggested that the phototoxicity of the new quinolones was related to DNA damage caused by reactive oxygen species, especially 1O2.

Characterization of acetohexamide reductases purified from rabbit liver, kidney, and heart: structural requirements for substrates and inhibitors

The structural requirements of acetohexamide reductases purified from rabbit liver, kidney, and heart for substrates and inhibitors were examined. Acetohexamide, an oral antidiabetic drug with a ketone group, and analogs of it with various alkyl groups instead of the cyclohexyl group were used as substrates for these three enzymes. The results obtained as to substrate specificity suggested that the nature of the substrate-binding region of the heart enzyme is markedly different from those of the substrate-binding regions of the liver and kidney enzymes. Tolbutamide, which has no ketone group within its chemical structure, strongly inhibited the heart enzyme, whereas it had little ability to inhibit the liver or kidney enzyme. The inhibition of the heart enzyme by tolbutamide was competitive with respect to acetohexamide and uncompetitive with respect to NADPH. Furthermore, tolbutamide analogs with n-pentyl and n-hexyl groups instead of the n-butyl group exhibited very pronounced inhibition of only the heart enzyme. Therefore, it is reasonable to postulate that the heart enzyme, unlike the liver and kidney ones, has a cleft of a strongly hydrophobic nature near its substrate-binding region, and that this hydrophobic cleft plays a critical role in the interaction of the heart enzyme with the cyclohexyl group of acetohexamide.

Singlet oxygen (1 delta g) generation from coproporphyrin in Propionibacterium acnes on irradiation

Although singlet oxygen has been postulated to be a highly reactive and toxic intermediate, there has been no evidence of considerable generation of singlet oxygen in vivo level except for special cases. In this work, we firstly measured the near-infrared emission spectra corresponding to the O2(1 delta g) --> O2(3 epsilon g-) transition of singlet oxygen of cutaneous Propionibacterium acnes (P. acnes) porphyrin under laser excitation. A comparison of the singlet oxygen production of coproporphyrin, which is produced predominantly from P. acnes, with that of other photosensitizers revealed coproporphyrin to be a highly efficient singlet oxygen generator under ultraviolet light A irradiation on the skin. These results suggest that singlet oxygen can be generated on the skin surface from P. acnes porphyrin under ultraviolet irradiation and induce serious damage to the skin.

Purification and catalytic properties of a novel acetohexamide-reducing enzyme from rabbit heart

An enzyme catalyzing the metabolic reduction of acetohexamide [4-acetyl-N-(cyclohexyl-carbamoyl)benzenesulfonamide], an oral antidiabetic drug, was purified to homogeneity from the cytosolic fraction of rabbit heart. The molecular mass of the purified enzyme was estimated to be 110 kDa by gel filtration and nondenaturing PAGE and 28 kDa by SDS-PAGE, suggesting that the enzyme is composed of four identical-size subunits. 4-Benzoyl-pyridine and p-nitroacetophenone, typical substrates of carbonyl reductase [EC 1.1.1.184], were not reduced by the enzyme. Of drugs with a ketone group tested, only acetohexamide was a good substrate of the enzyme. the enzyme effectively reduced analogs substituted with various alkyl groups instead of the cyclohexyl group in acetohexamide, although it had little or no ability to reduce analogs substituted with various alkyl groups instead of the methyl group in acetohexamide. The enzyme was inhibited not only by quercetin, a well-known inhibitor of carbonyl reductase, but also by phenobarbital, a potent inhibitor of aldehyde reductase [EC 1.1.1.2]. These results indicate that the enzyme purified from rabbit heart is a novel enzyme responsible for the reduction of acetohexamide and its analogs.

Measurement of 1268 nm emission for comparison of singlet oxygen (1 delta g) production efficiency of various dyes

Singlet oxygen generation from laser-excited photosensitive dyes was measured directly using a sensitive near-infrared emission spectrometer to monitor the O2(1 delta g)-->O2(3 sigma -g) transition at 1268 nm. The emission intensity was proportional to both the laser power and the concentration of the dyes. The singlet oxygen producing ability of the dyes was compared with that of eosin YS as a standard in methanol. The relative efficiencies of singlet oxygen generation were determined for rose bengal, erythrosine B, phloxine B and eosin YS as 2.39, 1.73, 1.38, 1.00, respectively, while uranine showed no emission in this spectral region. Using rose bengal, erythrosine B, phloxine B and eosin YS, the efficiency of singlet oxygen generation correlated with the photobleaching reaction rate of azo-dyes by these dyes, suggesting singlet oxygen to be a species responsible for causing the photobleaching of azo-dyes. The halogen substituent effect on the efficiency of singlet oxygen generation from laser-excited photosensitive dyes was also examined systematically.

Contributions of human long-wave and middle-wave cones to motion detection

1. It has been suggested that motion may be best detected by the luminance mechanism. If this is the most sensitive mechanism, motion thresholds may be used to isolate the luminance mechanism and study its properties. 2. A moving (1 cycle deg-1), vertical, heterochromatic (red-plus-green), foveal grating was presented on a bright yellow (577 nm wavelength) field. Detection and motion (direction identification: left versus right) thresholds were measured for different amplitude ratios of the red and green components spatially summed in phase or in antiphase. Threshold contours plotted in cone-contrast co-ordinates (L',M') for the long-wave (L) and middle-wave (M) cones, revealed two motion mechanisms: a luminance mechanism that responds to a weighted sum of L and M contrasts, and a spectrally opponent mechanism that responds to a weighted difference. 3. Detection and motion thresholds, measured at 1-4 Hz, were identical for luminance gratings, having equal cone contrasts, L' and M', of the same sign. For chromatic gratings, with L' and M' of opposite sign, motion thresholds were higher than detection thresholds. A red-green hue mechanism may mediate chromatic detection, and a separate spectrally opponent motion mechanism may mediate motion. 4. The red-green hue mechanism was assessed from 1 to 15 Hz with an explicit hue criterion. The detection contour had a constant slope of one, implying equal L' and M' contributions of opposite sign. For motion identification, L' and M' contributed equally at 1 Hz, but the M' contribution was attenuated at higher velocities. 5. The cone-contrast metric provides a physiologically relevant comparison of sensitivities of the two motion mechanisms. At 1 Hz, the spectrally opponent motion mechanism is approximately 4 times more sensitive than the luminance mechanism. As temporal frequency is increased, the relative sensitivities change so that the luminance mechanism is more sensitive above 9 Hz. 6. The less sensitive motion mechanism was isolated with a quadrature phase protocol, using a pair of heterochromatic red-plus-green gratings, counterphase flickering in spatial and temporal quadrature phase with respect to each other. One grating was set slightly suprathreshold and oriented in cone contrast (L',M') so as to potentiate a single motion mechanism, the sensitivity of which was probed with the second grating, which was varied in (L',M'). This allowed us to measure the motion detection contour of the less sensitive luminance mechanism at low velocities.(ABSTRACT TRUNCATED AT 400 WORDS)

Combined testosterone treatment in pubertal and adult periods induces male-specific acetohexamide reductase activity in liver microsomes of female rats

The influence of testosterone treatment on acetohexamide reductase activities in liver microsomes and cytosol of female rats was examined. Acetohexamide reductase activity in liver microsomes was much lower in female rats than in male rats. Combined testosterone treatment in pubertal and adult periods induced male-specific acetohexamide reductase activity in liver microsomes of female rats. However, testosterone treatment only during puberty or during adulthood was without effect. Testosterone secreted from the testes during puberty appeared to have a significant effect similar to neonatal imprinting in the induction of acetohexamide reductase activity in liver microsomes of female rats. The combined testosterone treatment, or testosterone treatment only during puberty or during adulthood had no effect on acetohexamide reductase activity in liver cytosol of female rats.

Sex-related differences of acetohexamide reductase activities in the liver and kidney of various mammalian species

Sex-related differences of acetohexamide reductase activities in cytosol and microsomes from the liver and kidney of the rat, mouse, guinea pig, hamster and rabbit were examined. Among animal species tested, the rat, guinea pig and rabbit exhibited sex-related differences in the activities. The activities in liver cytosol of the rat and rabbit were higher in the females than in the males, whereas the activity in kidney cytosol of the rabbit was higher in the male than in the female. Furthermore, the activities in liver and kidney microsomes of the rat and that in kidney microsomes of the guinea pig were much higher in the males than in the females. It is interesting to note that significant sex-related differences of acetohexamide reductase activities are found in some animal species other than the rat.

Primary osteosarcoma of the ovary. A case report

A case of primary osteosarcoma arising in the left ovary of a 75-year-old female is described. The chief complaint was a sensation of lower abdominal mass. An abdominal plain film showed a large calcified mass in pelvic region, and a preoperative diagnosis of "ovarian fibroma" was made. The excised tumor was divided into 4 pieces, resembling an oyster shell. Microscopically, the tumor fragments were composed of compact bone or woven bone with surrounding atypical osteoblasts and osteoclasts. The tumor was partly composed of numerous spindle cells with malignant osteoid or atypical chondroid formation, and diagnosed as "osteosarcoma". The cystic part of the lesion was lined with a single layer of columnar cells, but the tumor contained no other germ elements or stem cells, or malignant epithelium. Therefore, it is doubtful that this tumor originated from teratoma or malignant mixed mesodermal tumor, and we conclude that this ovarian osteosarcoma arose through a neoplastic change in ovarian stromal cells. The patient died 4 months after surgery due to intra-abdominal and intrathoracic dissemination of the tumor.