Calcium regulation by troponin and its genetic disorder in striated muscle contraction

Contraction of skeletal and cardiac muscles is regulated by Ca2+ through specific Ca(2+)-regulatory proteins, troponin and tropomyosin, located in the thin filament. Troponin is a Ca2+ receptive protein consisting of three differet components, troponins C, I, and T. The essential mechanisms of Ca(2+)-regulation are the inhibition of contractile interaction between myosin and actin by the inhibitory action of troponin I and the reversal of the inhibition by troponin I through the Ca(2+)-binding to troponin C. All three components of troponin are required for the Ca(2+)-regulation of contraction. This article reviews following aspects of troponin researches: 1) early studies on the structure and function of troponin, 2) molecular mechanisms of Ca(2+)-regulation, 3) principles of troponin-exchange in skinned fibers and properties of troponin isoforms thereafter clarified under physiological conditions, 4) recent studies on the functional consequences of the mutations in human cardiac troponins T and I that cause genetic disorders, familial hypertrophic cardiomyopathy (HCM), and familial dilated cardiomyopathy (DCM).     

Tumor-specific novel taxoid-monoclonal antibody conjugates

Taxoids bearing methyldisulfanyl(alkanoyl) groups for taxoid-antibody immunoconjugates were designed, synthesized and their activities evaluated. A highly cytotoxic C-10 methyldisulfanylpropanoyl taxoid was conjugated to monoclonal antibodies recognizing the epidermal growth factor receptor (EGFR) expressed in human squamous cancers. These conjugates were shown to possess remarkable target-specific antitumor activity in vivo against EGFR-expressing A431 tumor xenografts in severe combined immune deficiency mice, resulting in complete inhibition of tumor growth in all the treated mice.     

Catechol and hydroquinone have different redox properties responsible for their differential DNA-damaging ability.

We examined the redox properties of the "carcinogenic" catechol and the "noncarcinogenic" hydroquinone in relation to different DNA damaging activities and carcinogenicity using 32P-labeled DNA fragments obtained from the human genes. In the presence of endogenous NADH and Cu2+, catechol induces stronger DNA damage than hydroquinone, although the magnitudes of their DNA damaging activities were reversed in the absence of NADH. In both cases, DNA damage resulted from base modification at guanine and thymine residues in addition to strand breakage induced by Cu+ and H2O2, generated during the oxidation of catechol and hydroquinone into 1,2-benzoquinone and 1,4-benzoquinone, respectively. EPR and 1H NMR studies indicated that 1,2-benzoquinone is converted directly into catechol through a nonenzymatic two-electron reduction by NADH whereas 1,4-benzoquinone is reduced into hydroquinone through a semiquinone radical intermediate through two cycles of one-electron reduction. The reduction of 1,2-benzoquinone by NADH proceeds more rapidly than that of 1,4-benzoquinone. This study demonstrates that the rapid 1,2-benzoquinone two-electron reduction accelerates the redox reaction turnover between catechol and 1,2-benzoquinone, resulting in the enhancement of DNA damage. These results suggest that the differences in NADH-mediated redox properties of catechol and hydroquinone contribute to their different carcinogenicities.     

Role of hypomagnesemia in chronic cyclosporine nephropathy

BACKGROUND: Hypomagnesemia is a common finding of cyclosporine (CsA)-treated patients and has been proposed as both a cause and a consequence of CsA-induced nephrotoxicity. This experiment was conducted to elucidate the role of hypomagnesemia in the pathogenesis of chronic CsA nephropathy. METHODS: CsA (15 mg/kg/day subcutaneously) was administered to rats maintained on a low-sodium diet for 1, 2, and 4 weeks, and the effects of magnesium (Mg) supplementation on renal function, renal histology, and renal gene expression profile of fibrogenic molecules and vasoconstrictors was examined. RESULTS: CsA elicited hypomagnesemia and induced a progressive decline in glomerular filtration. At 28 day, renal tubular atrophy and cortical striped interstitial fibrosis were evident with CsA treatment. Dietary supplementation of Mg ameliorated CsA-induced hypomagnesemia and almost completely abolished CsA-induced chronic fibrotic lesions. Neither CsA nor Mg supplementation affected blood pressure. Renal cortical mRNA of transforming growth factor beta, plasminogen activator inhibitor (PAI)-1, and extracellular matrix started to increase at 14 days and elevated further at 28 days. In contrast, the increase in mRNA of tissue inhibitor of matrix metalloproteinase-1 and renin was evident early at 7 days and reached peak at 14 days. These mRNA increases, except that of renin, were almost abolished when hypomagnesemia was corrected. Magnesium supplementation also improved glomerular dysfunction, at least in part, through inhibition of up-regulated mRNA of endothelin-1. CONCLUSION: CsA-induced hypomagnesemia contributes to chronic renal fibrotic lesions seen during CsA treatment through up-regulation of fibrogenic molecules, most notably early activation of tissue inhibitor of matrix metalloproteinase-1 expression.     

Pseudoxanthoma elasticum (PXE)-like calcification in adult dermatomyositis

A case of pseudoxanthoma elasticum (PXE)-like calcification in adult dermatomyositis (DM) is described. The patient was a 38-year-old woman with a history of dermatomyositis for 3 months. Yellowish, hard, papulo-plaque lesions, which looked like those of pseudoxanthoma elasticum, were noted on her left axilla. Calcium deposition was confirmed by X-ray, histopathological, and electron microscopic examinations. Histopathological and histochemical examinations showed acicular calcium deposition in the middle and deep dermis surrounded by mucin. Electron microscopic examination revealed that the calcium deposition was not on collagen fibers. These morphological features were distinct from those of PXE. We proposed the possibility that degenerated mucin or degenerated elastic fiber might result in subsequent calcium deposition in reticular calcinosis in adult DM. The calcification clinically disappeared without any specific treatment except for prednisolone and cyclophosphamide.     

New bone-seeking agent: Animal study of Tc-99m-incadronate

OBJECTIVE: Disodium cycloheptylaminomethylenediphosphonate monohydrate (incadronate disodium) is a third-generation bisphosphonate compound which potently inhibits bone resorption, and a highly effective drug in the treatment of metastatic bone disease. We first labeled incadronate disodium with 99mTc, and examined its biodistribution and bone uptake after intravenous injection in rats to assess its potential for clinical use as a bone-seeking agent for judgment of the therapeutic effect of incadronate on bone metastases. Bone scan with 99mTc-labeled incadronate (99mTc-incadronate) may yield important information prior to the use of incadronate for treatment of bone metastases. METHODS: Synthesis of 99mTc-incadronate was carried out by reduction of 99mTc-pertechnetate in the presence of SnCl2 and N2 gas. Normal rats were injected with 18.5 MBq (0.5 mCi) 99mTc-incadronate in a volume of 0.1 ml intravenously and then sacrificed at 15 min, 30 min, 1 h or 2 h (six rats at each time point) after injection. Samples of muscle, stomach, small intestine, kidney, liver and bone (femur) were taken and weighed. In addition, a 1-ml sample of blood was drawn from the heart, and urine was taken from the urinary bladder immediately after sacrifice. Samples were measured for radioactivity and expressed as percent uptake of injected dose per gram or per milliliter (% ID/g or ml). Bone-to-blood and bone-to-muscle uptake ratios were determined from the % ID/g or ml values for these organs. RESULTS: The greatest accumulation of 99mTc-incadronate was found in bone. Radioactivity in bone was as high as 3.22 +/- 0.68% ID/g at 2 hours after injection. Scintigraphic images of 99mTc-incadronate in normal rats revealed highly selective skeletal uptake. CONCLUSION: 99mTc-incadronate exhibited high uptake in bone, and relatively low uptake in soft tissue, suggesting that it may be useful as a bone-seeking agent for judgment of the therapeutic effect of incadronate on bone metastases, by determining the degree of its accumulation in metastatic bone lesions.     

Microarray studies of gene expression in circulating leukocytes in kidney diseases

The molecular characterization of changes in mRNA expression in renal tissue during disease is hampered by the acquisition of sufficient mRNA to do genomewide expression profiling. In many renal diseases, such as systemic lupus erythematosus, IgA nephropathy, antineutrophil cytoplasmic autoantibody (ANCA) associated glomerulonephritis, and small-vessel vasculitis (ANCA disease), circulating leukocytes play a role in onset, progression, and severity of the condition. Circulating leukocytes are readily isolated and supply sufficient mRNA for analysis, allowing molecular investigation into their involvement in the disease process. Our laboratory has undertaken a systematic study of the genomewide expression profiles of the circulating leukocytes from patients with a variety of renal diseases (ANCA disease, IgA nephropathy, lupus nephritis, focal segmental glomerulosclerosis), using the Affymetrix high-density gene chip array technology. Analysis of the data showed clustering of expressed genes unique for each individual disease group. These results imply that significant gene expression changes occur in leukocytes that are circulating in patients with renal diseases. In addition, gene expression has been studied in leukocytes activated in vitro by mechanisms that mimic pathogenic events in vivo. The expression levels of genes identified in in vitro studies were compared with the patient leukocyte gene expression to determine whether similar pathological events were occurring in vivo.     

Phase II study of twice-daily high-dose thoracic radiotherapy alternating with cisplatin and vindesine for unresectable stage III non-small-cell lung cancer: Japan Clinical Oncology Group Study 9306.

PURPOSE: To evaluate the efficacy and toxicity of high-dose thoracic radiotherapy (TRT) alternating with chemotherapy (CH) for unresectable stage III non--small-cell lung cancer (NSCLC). PATIENTS AND METHODS: Forty-one patients received TRT with 1.5 Gy twice daily, 5 days a week, on weeks 1, 2, 5, 6, and 9, up to a total dose of 66 to 72 Gy, alternating with cisplatin 80 mg/m(2) on day 1 and vindesine 3 mg/m(2) on days 1 and 8, repeated every 4 weeks, for two or three courses beginning on week 3. RESULTS: The median (range) total dose of TRT and number of CH courses were 72 Gy (16.5 to 72 Gy) and three (zero to three), respectively. Delay in TRT > or = 5 days was observed in 24 (75%) of 32 patients who completed the projected treatment, due to leukopenia in 12, esophagitis in seven, infection in two, and other causes in three patients. Partial responses were obtained in 36 patients (88%). The median survival time and 3- and 5-year survival rates were 18.4 months, 24%, and 10%, respectively. Grade 3 or 4 leukopenia and esophagitis developed in 32 and seven patients, respectively. Grade 3 or 4 late esophageal toxicity developed in two patients. CONCLUSION: Alternating high-dose TRT and CH for stage III NSCLC produced a high response rate with median and long-term survival comparable to prior trials utilizing standard approaches in this population. Acute and late esophageal toxicity was observed and interruption of TRT was required in most of the patients.     

Immunohistochemical assessment of localization and frequency of micrometastases in lymph nodes of colorectal cancer.

PURPOSE: Micrometastases are often found in regional lymph nodes of colorectal cancer (CRC). The aim of this study is to examine the extent and distribution of such lymph nodes. EXPERIMENTAL DESIGN: We immunohistochemically assessed localization and frequency of micrometastases in 878 lymph nodes from 98 patients with CRC. The anatomical position of lymph nodes was defined as level 1 to level 3 according to distance from the main tumor. RESULTS: The frequency of micrometastasis increased through observation of the 4-microm-thick lymph node sections, from one to two to five slices. With five slices, micrometastasis was frequently and extensively present in 49.1, 35.7, and 53.3% patients of histologically node-negative patients, node-positive patients at level 1, and node-positive patients at level 2, respectively. We then assessed the value of the presence of micrometastasis in node-negative patients with regard to prognosis, but no significant impact was obtained. To examine the reproducibility of the results obtained with immunohistochemistry, serial sectioning (four consecutive slices at seven different levels) of lymph nodes was additionally performed in lymph nodes initially diagnosed as micrometastasis positive. Immunohistochemical detection revealed that the sectioning level highly affected the results. CONCLUSIONS: Our results indicated frequent presence of micrometastasis in lymph nodes of CRC and that micrometastasis in node-negative CRC patients did not help in predicting the outcome, in part because of the limited reproducibility with immunohistochemistry.