Involvement of protein kinase C in taxol-induced polyploidization in a cultured sarcoma cell line

Muscle pain in models of chemotherapy-induced and alcohol-induced peripheral neuropathy

OBJECTIVE

While inflammatory pain is well described in skeletal muscle, neuropathic muscle pain remains to be clarified. We used 3 well-established rodent models of peripheral neuropathy to evaluate for muscle pain.

METHODS

In rats exposed to either of 2 neurotoxic cancer chemotherapies, paclitaxel or oxaliplatin, or to alcohol consumption, we assessed the evolution of mechanical hyperalgesia in skeletal muscle and skin, in the same animal. To explore the involvement of protein kinase C epsilon (PKCε), a second messenger implicated in some forms of neuropathic pain, antisense oligodeoxynucleotides (AS-ODNs) or mismatch ODNs (MM-ODNs) for PKCε were administered intrathecally.

RESULTS

Rats submitted to models of chemotherapy-induced and alcohol-induced neuropathy developed persistent muscle hyperalgesia, which evolved in parallel in muscle and skin. The administration of PKCε AS, which has been shown to mediate cutaneous hyperalgesia in paclitaxel and ethanol models of neuropathic pain, also inhibited muscle hyperalgesia induced by these agents. Stopping AS-ODN was associated with the reappearance of hyperalgesia at both sites. The AS-ODN to PKCε treatment was devoid of effect in both muscle and skin in the oxaliplatin neuropathy model.

INTERPRETATION

Our results support the suggestion that neuropathic muscle pain may be a greater clinical problem than generally appreciated.

Phorbol myristate induces apoptosis of taxol-resistant sarcoma cells in vitro

Taxol was found to induce polyploidization and apoptosis in cultured methylcholanthrene-induced sarcoma cells (Meth-A cells), but some of the cells in G1 phase were not affected. We refer to these cells as taxol-resistant cells. Phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) regulator, was used to test the taxol-resistant cells. Many of the taxol-resistant cells disappeared after treatment with taxol in the presence of PMA. To explore the mechanism of this effect, we employed flow cytometry to determine levels of p53, p21, bcl-2 and caspase proteins in the taxol-resistant cells, and found that the expression of the bcl-2 protein was markedly decreased and the expression of the caspase protein markedly increased after treatment with taxol in the presence of PMA. These findings suggest that PMA enhances the sensitivity of taxol-resistant cells to taxol, and taxol treatment in the presence of PMA induces the apoptosis of taxol-resistant cells by inhibiting the expression of the bcl-2 protein and increasing the expression of the caspase protein.

Amiodarone minimizes experimental autoimmune myocarditis in rats

Amiodarone, a promising drug for the treatment of tachyarrythmias, was recently found to have immunomodulatory effects in vitro. We hypothesized that amiodarone would affect the immune system in vivo and examined the effect of amiodarone on myocarditis in rats. We induced experimental autoimmune myocarditis in rats by cardiac myosin immunization and treated the animals with an intraperitoneal injection of amiodarone at 25 mg/kg/every other day, 10 times after the induction of experimental autoimmune myocarditis. In the treated group, both microscopic and macroscopic examinations showed reduced heart weights, a mild and localized infiltration of inflammatory cells and fibrosis in the myocardium, and a mild congestion in the liver and lungs as compared with the control group. The phenotypic distribution of lymphocytes in peripheral blood showed a significant decrease in the CD4/CD8a ratio in the treated group, but not in the control group. The proportion of mast cells involved in inflammatory cell infiltration was lower in the treated group than the control group. In vitro, amiodarone inhibited the proliferation of mast cells by arresting them in the G2 phase of the cell cycle. These results indicated that amiodarone minimized the progression of experimental autoimmune myocarditis, suggesting a potential therapeutic role for amiodarone treatment in patients suffering from myocarditis, especially myocarditis complicated by cardiac arrhythmias. One possible mechanism by which amiodarone minimizes the progression of experimental autoimmune myocarditis may be to affect the immune system via the immunomodulatory effects on T cell and mast cell functions.

Octaploid Meth-A cells are established from a highly polyploidized cell population

Tetraploid Meth-A cells were polyploidized by demecolcin, an inhibitor of spindle fibre formation in M phase, and then released from the drug 1, 2, 3 and 4 days after the addition. Octaploid cells were successfully established from cell populations including hexadecaploid cells produced by 2, 3 and 4 days of exposure to demecolcin. One-day-treated cells were polyploidized octaploid cells, but they returned to tetraploid cells. All of the octaploid Meth-A cells showed essentially the same features. The octaploid Meth-A cells had eight homologous chromosomes and double the DNA content of the parent tetraploid cells. The doubling time of octaploid Meth-A cells was 30.2 h, somewhat longer than the 28.3 and 24.0 h of tetraploid and diploid cells, respectively. The fractions of cells in the G1, S and G2/M phases were essentially the same in diploid, tetraploid and octaploid Meth-A cells. The cell volume of octaploid Meth-A cells was about two times that of the tetraploid cells. It was concluded that octaploid Meth-A cells were established from transient hexadecaploid cells produced by the polyploidization of tetraploid cells that had been established from diploid cells.

Role of protein kinase Cepsilon and protein kinase A in a model of paclitaxel-induced painful peripheral neuropathy in the rat

The clinical use of the antineoplastic agent paclitaxel (Taxol) is significantly limited in its effectiveness by a dose-related painful peripheral neuropathy. To evaluate underlying mechanisms, we developed a model of Taxol-induced painful peripheral neuropathy in the rat and determined the involvement of two second messengers that contribute to enhanced nociception in other models of inflammatory and neuropathic pain, protein kinase Cepsilon and protein kinase A. Taxol administered acutely, or chronically over 12 days, produced a decrease in mechanical nociceptive threshold. Acutely, Taxol induced hyperalgesia that was significant within 1 h, maximal after 6 h and resolved completely by 24 h after a single treatment. Chronically, Taxol treatment resulted in a dose (0.1-1 mg/kg/day)-dependent decrease in nociceptive threshold, measured 24 h after administration, maximal within 5 days from the commencement of Taxol administration and resolving by 2 weeks after the last dose of Taxol. Chronic Taxol treatment also increased the number of action potentials evoked by sustained (60-s) threshold and suprathreshold (10-g) stimulation of a sub-population of C-fibers in rats with Taxol-induced hyperalgesia. Mechanical allodynia and thermal hyperalgesia were also present in Taxol-treated rats. Hyperalgesia, produced by both acute and chronic Taxol, was attenuated by intradermal injection of selective second messenger antagonists for protein kinase Cepsilon and protein kinase A. These findings provide insight into the mechanism of Taxol-induced painful peripheral neuropathy that may help control side effects of chemotherapy and improve its clinical efficacy.

Selective enhanced phosphorylation of shrimp beta-tubulin by PKC-delta with PEP(taxol), a synthetic peptide encoding the taxol binding region

Beta-tubulin cDNA from the shrimp Penaeus japonicus was isolated by homology cloning. Expression of cDNA in Escherichia coli yielded a 55 kDa polypeptide, positive for monoclonal antibodies against mammalian beta-tubulin. Autoradiography demonstrated the bacterially expressed hepatopancreas beta-tubulin of P. japonicus is specifically phosphorylated by the delta isoenzyme of protein kinase C (PKC-delta) purified from the plasma membrane of the shrimp heart, in the presence of the receptor for activated PKC (RACK), but not in its absence. Purified shrimp heart PKC-delta is able to phosphorylate bacterially expressed shrimp beta-tubulin without the presence of Ca(++), but requires Mg(++). The kinase activity of purified PKC-delta on bacterially expressed beta-tubulin was enhanced by incubation with PEP(taxol), a synthetic peptide encoding the taxol-binding region of beta-tubulin. In other words, PEP(taxol) modulates the kinase activity of PKC-delta through RACK.

Temperature dependence in proliferation of tetraploid Meth-A cells in comparison with the parent diploid cells

The temperature dependency for the growth of tetraploid Meth-A cells established from diploid cells was examined in comparison with the parent diploid cells. Proliferation of the tetraploid cells was markedly suppressed below 35 degrees C. At above 40 degrees C, both the diploid and tetraploid Meth-A cells ceased growing. Flow cytometry (FCM) analysis showed that the hyperploid cell fraction increased in the tetraploid Meth-A cell population at low temperatures. The fluidity of cell membranes at different temperatures was measured by means of electron spin resonance (ESR), and it was almost the same between the diploid and tetraploid Meth-A cells. It was suggested that the decreased proliferation below 35 degrees C of the tetraploid Meth-A cells might be due to the increased volume of the cells.

Growth hormone interferes with the progression of myocarditis in rats

In this study, we investigated whether recombinant human growth hormone (rhGH) influences the progression of myocarditis. We induced experimental autoimmune myocarditis in F344 rats by subcutaneous injection of cardiac myosin, and divided the rats into three groups: (1) control group, saline injection; (2) pre-treated group, subcutaneous injection of rhGH (100 mIU/rat/day for 10 days) before induction of experimental autoimmune myocarditis; and (3) post-treated group, subcutaneous injection of rhGH (100 mIU/rat/day for 10 days) after induction of experimental autoimmune myocarditis. On the 35th day after induction of experimental autoimmune myocarditis, all rats were sacrificed and the hearts were examined. The increase in body weight was smaller in the control group than the pre-treated group and the rate of heart weight/body weight was larger in the control group than in the two treated groups. Histopathologically, rats in the control group showed multifocal infiltration by inflammatory cells, mainly neutrophils, lymphocytes and macrophages, extensive fibrosis, and a higher proportion of mast cells in the inflamed region. In contrast, rats in the two treated groups showed only minor changes. We found that rhGH did not influence the distribution of lymphocytes in peripheral blood in the three groups, and that rhGH induced G1 checkpoint dysfunction, thereby arresting the cell cycle in G1 and inhibiting the proliferation of mast cells in vitro. These findings suggest a possible role for mast cells in the progression of myocarditis and the rhGH may be a candidate for use as a new tool to treat myocarditis.