Large-scale propagation of a replication-defective adenovirus vector in stirred-tank bioreactor PER.C6 cell culture under sparging conditions

Large-scale propagation of replication-defective adenovirus vectors has not been well studied to date. One of the challenges for efficient propagation at large scale is to overcome the sensitivity of virus infected cells to gas sparging required for oxygenation and CO(2) removal. In our initial experiments, it was observed that productivity of an adenovirus vector was significantly reduced under sparging conditions as compared to nonsparged, i.e., surface-aerated controls in serum-free cultures. Investigations led to the identification of a buffer containing surfactant (Polysorbate-80, PS-80) that was included in the virus seed stock formulation and introduced through virus infection into the culture at a very low concentration as the cause of the reduced virus productivity. This finding was not obvious and trivial, as neither uninfected sparged nor infected nonsparged PER.C6 trade mark cells in serum-free cultures were affected by the buffer at such a low PS-80 concentration of 0.00025% (v/v), which is a common component of serum-free cell culture media. These results strongly suggest that virus-infected cells behave very differently from uninfected cells under sparging conditions. To mitigate the deleterious effects of sparging, the virus seed stock was prepared in the absence of the buffer containing PS-80. At the same time, the concentration of Pluronic-F68 (PF-68) in the serum-free medium was increased to 1 g/L, at which cell growth and metabolism were unaffected, even though this measure alone did not result in virus productivity improvement. Only by implementing the two measures together was virus productivity loss completely eliminated under sparging conditions. After demonstration of the process robustness in 2-L bioreactors, this adenovirus propagation process was successfully scaled up to 250 L in a 300-L bioreactor under the worst-case sparging conditions projected for 10,000-L scale.     

Serum-free suspension cultivation of PER.C6(R) cells and recombinant adenovirus production under different pH conditions

PER.C6(R) cell growth, metabolism, and adenovirus production were studied in head-to-head comparisons in stirred bioreactors under different pH conditions. Cell growth rate was found to be similar in the pH range of 7.1-7.6, while a long lag phase and a slower growth rate were observed at pH 6.8. The specific consumption rates of glucose and glutamine decreased rapidly over time during batch cell growth, as did the specific lactate and ammonium production rates. Cell metabolism in both infected and uninfected cultures was very sensitive to culture pH, resulting in dramatic differences in glucose/glutamine consumption and lactate/ammonium production under different pH conditions. It appeared that glucose metabolism was suppressed at low pH but the efficiency of energy production from glucose was enhanced. Adenovirus infection resulted in profound changes in cell growth and metabolism. Cell growth was largely arrested under all pH conditions, while glucose consumption and lactate production were elevated post virus infection. Virus infection induced a reduction in glutamine consumption at low pH but an increase at high pH. The optimal pH for adenovirus production was found to be 7.3 under the experimental conditions used in the study. Deviations from this optimum resulted in significant reductions of virus productivity. The results indicate that culture pH is a very critical process parameter in PER.C6(R) cell culture and adenovirus production.     

Enhanced values of the RBE and H ratio for cytogenetic effects induced by secondary electrons from an X-irradiated gold gurface

The low-energy secondary electrons emerging from the entrance surface of an X-irradiated gold foil increase the dose to cells in contact with or at micrometer distances from this surface (Radiat. Res. 150, 92-100, 1998). We examined the effect of the spectrum of these low-energy electrons on the RBE for cytogenetic effects and showed that this RBE was increased. A monolayer of surface-attached human T lymphocytes was exposed to 60 kV X rays in the absence or presence of a gold foil positioned immediately behind the cell layer or separated from it by a Mylar foil 0.9 or 2 microm thick. The enhancement of dose in the cell nuclei caused by the photoelectrons and Auger electrons emerging from the entrance surface of the gold foil was measured by TSEE dosimetry. Dose enhancement factors of 55.7, 46.6 and 37.5 were obtained with 0, 0.9 and 2 microm of Mylar inserted between the gold surface and the cell layer. This large enhancement results from the photoelectric effect in the gold foil, as shown by the accompanying Monte Carlo calculations of the secondary electron spectra at the gold surface. Auger electrons from the gold foil generally were not able to penetrate into the cell nuclei except for that fraction of the cells that had a very thin (< 0.7 microm) layer of cytoplasm and membranes between gold surface and cell nucleus. The dose-yield curves for dicentric chromosomes plus centric rings and for acentric fragments obtained after exposures without or with the gold foil were linear-quadratic. The coefficient alpha, the slope of the linear yield component, was increased in the presence of the gold foil and showed RBE values ranging from 1.7 to 2.2 compared to exposures in absence of the gold foil. The ratio of the yield of interstitial deletions and dicentrics (H ratio) was significantly increased from about 0.17 in the absence of the gold foil to about 0.22 in the presence of the gold foil. The increases in the RBE and the H ratio are interpreted in microdosimetric terms: The preferred occurrence of electron track ends in the vicinity of the gold surface causes an increase in the dose-mean restricted linear energy transfer in cell nuclei exposed to the photoelectrons and Auger electrons.     

Developmentally induced changes of the proteome in the protozoan parasite Leishmania donovani

In order to proceed through their life cycle, protozoan parasites of the genus Leishmania cycle between sandflies and mammals. This change of environment correlates with the differentiation from the promastigote stage (insect form) to the amastigote stage (intracellular mammalian form). The molecular basis underlying this major transformation is poorly understood so far; however, heat shock protein 90 (HSP90) appears to play a pivotal role. To further elucidate this process we identified proteins expressed preferentially in either of the two life cycle stages. By using two-dimensional (2-D) gel electrophoresis we observed defined changes in the protein pattern. A total of approximately 2000 protein spots were visualized. Of these, 31 proteins were present only in promastigotes. The abundance of 65 proteins increased during heat-induced in vitro amastigote differentiation, while a decreased abundance is observed for four proteins late in amastigote differentiation. Further analyses using matrix-assisted laser desorption/ionization-time of flight mass spectrometry and peptide mass fingerprinting 67 protein spots were identified representing 41 different proteins known from databases and eight hypothetical proteins. Further studies showed that most of the stage-specific proteins fall into five groups of functionally related proteins. These functional categories are: (i) stress response (e.g. heat, oxidative stress); (ii) cytoskeleton and cell membrane; (iii) energy metabolism and phosphorylation; (iv) cell cycle and proliferation; and (v) amino acid metabolism. Very similar changes in the 2-D protein pattern were obtained when in vitro amastigote differentiation was induced either by pharmacological inhibition of HSP90 or by a combination of heat stress and acidic pH supporting the critical role for HSP90 in life cycle control.     

Heart and liver defects and reduced transforming growth factor beta2 sensitivity in transforming growth factor beta type III receptor-deficient embryos

The type III transforming growth factor beta (TGFbeta) receptor (TbetaRIII) binds both TGFbeta and inhibin with high affinity and modulates the association of these ligands with their signaling receptors. However, the significance of TbetaRIII signaling in vivo is not known. In this study, we have sought to determine the role of TbetaRIII during development. We identified the predominant expression sites of TbetaRIII mRNA as liver and heart during midgestation and have disrupted the murine TbetaRIII gene by homologous recombination. Beginning at embryonic day 13.5, mice with mutations in TbetaRIII developed lethal proliferative defects in heart and apoptosis in liver, indicating that TbetaRIII is required during murine somatic development. To assess the effects of the absence of TbetaRIII on the function of its ligands, primary fibroblasts were generated from TbetaRIII-null and wild-type embryos. Our results indicate that TbetaRIII deficiency differentially affects the activities of TGFbeta ligands. Notably, TbetaRIII-null cells exhibited significantly reduced sensitivity to TGFbeta2 in terms of growth inhibition, reporter gene activation, and Smad2 nuclear localization, effects not observed with other ligands. These data indicate that TbetaRIII is an important modulator of TGFbeta2 function in embryonic fibroblasts and that reduced sensitivity to TGFbeta2 may underlie aspects of the TbetaRIII mutant phenotype.     

Anaerobic utilization of essential oils bydenitrifying bacteria

Plant volatile organic compounds are a major carbonsource in nature. We studied the degradability ofthese substances by anaerobic microorganisms inenrichment cultures with representative essential oilsas organic substrates and nitrate as electronacceptor. Lemon and pine needle oil supportedmicrobial growth in the presence of pure oil, whereasparsley seed, camphor, sage, fennel, and mint oilsupported growth only when the essential oils weredissolved in an overlying phase of2,2,4,4,6,8,8-heptamethylnonane. Thyme oil did notsupport denitrification. Analyses of the microbiallydegraded oils revealed the disappearance ofmonoterpenes, of several monoterpenoids, and ofmethoxy-propenyl-benzenes, including apiole andmyristicin. Most-probable-number determinations fordenitrifying communities in sewage sludge and forestsoil yielded 10⁶ to 10⁷monoterpene-utilizing cells ml^-1, representing0.7 to 100% of the total cultivablenitrate-reducing microorganisms. The utilization ofessential oils together with the common occurrence ofthis metabolic trait are indications for anenvironmentally important, but currently unexploredanaerobic turnover of plant volatile organic compoundsin soil.     

Evidence for spontaneous postlactational estrus in gray short-tailed opossums (Monodelphis domestica)

Previous studies of the gray short-tailed opossum have shown that ovarian activity and estrus are induced by male pheromones, but we recently documented urogenital sinus (UGS) estrus in postlactational females despite their isolation from the male stimuli known to be associated with induced estrus. Body weights and UGS smears were collected after removal of pups in midlactation (19-37 days postpartum), after weaning (55-61 days postpartum), or after pheromone exposure. Estradiol was measured by RIA in plasma samples collected from dams during lactation, after separation from pups, and at estrus. Average days to UGS estrus from pup removal or initial pheromone exposure differed (P<0.05) only between the midlactation and pheromone exposure groups. Postlactational females showed a decrease in body weight from the time of pup removal or weaning to estrus, which contrasts with the increase seen in pheromonally stimulated females. Plasma estradiol was elevated at estrus in all groups, and females that were paired with males at postlactational estrus mated and produced litters. This study demonstrates that gray short-tailed opossums consistently experience estrus within 2 wk of weaning their young and that postlactational estrus appears to be hormonally and behaviorally equivalent to estrus induced by direct exposure to male pheromones.     

Role of cGMP versus 20-HETE in the vasodilator response to nitric oxide in rat cerebral arteries

This study examined the response to nitric oxide (NO) in rat middle cerebral arteries (MCA). NO donors increased the activity of a 205-pS K(+) channel recorded from vascular smooth muscle (VSM) cells isolated from MCA 10-fold. Blockade of guanylyl cyclase activity with 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) did not alter the effect of NO on this channel. In contrast, adding 20-hydroxyeicosatetraenoic acid (20-HETE) to the bath (10(-7) M) abolished the response to NO. NO donors also increased the diameter of serotonin-preconstricted MCA to 85% of control. Blockade of K(+) channels with iberiotoxin or a high-K(+) medium reduced this response by 50%. ODQ (10(-5) M) reduced this response by 47 +/- 3%, whereas preventing the fall of 20-HETE levels reduced the response by 59 +/- 2% (n = 5). Blockade of both pathways eliminated the response to NO donors. These results indicate that activation of K(+) channels contributes 50% to vasodilator response to NO in rat MCA. This is mediated by a fall in 20-HETE levels rather than a rise in cGMP levels or a direct effect of NO.