Infrared radiation properties of Ho³⁺ in multicomponent germanium tellurite glasses

Ho(3+)-doped and Ho(3+)/Yb(3+)-codoped multicomponent germanium tellurite (MGT) glasses with multifarious emission channels in the near-infrared wavelength region have been fabricated and characterized. Judd-Ofelt intensity parameters of Ho(3+)-doped MGT glasses are solved to be Ω2=5.32×10(-20)  cm(2), Ω(4)=2.73×10(-20)  cm(2), and Ω(6)=1.12×10(-20)  cm(2), indicating a higher asymmetric and stronger covalent environment around Ho(3+) ions in MGT glasses. Efficient infrared fluorescences have been observed in MGT glasses, and spontaneous emission probabilities are derived to be 230.4, 79.9, and 138.3  s(-1) for the (5)I(6)→(5)I(8), ((5)F(4),(5)S(2))→(5)I(5), and (5)I(7)→(5)I(8) radiative transitions, respectively. In Ho(3+)/Yb(3+)-codoped MGT glasses, the maximum stimulated emission cross-section of 2.0 μm emission is calculated to be 4.93×10(-21)  cm(2), and the corresponding gain cross-section is derived to be 3.62×10(-21)  cm(2) when the excited state population fraction P reaches 0.8. Multifarious infrared emissions show that Ho(3+) in MGT glasses is a good candidate for optical amplifiers and optoelectronic devices.

Pr3+-doped heavy metal germanium tellurite glasses for irradiative light source in minimally invasive photodynamic therapy surgery

Pr3+-doped medium-low phonon energy heavy metal germanium tellurite (NZPGT) glasses have been fabricated and the intense multi-peak red fluorescence emissions of Pr3+ are exhibited. Judd-Ofelt parameters Ω2 = 3.14 × 10(-20)cm(2), Ω4 = 10.67 × 10(-20)cm(2) and Ω6 = 3.95 × 10(-20)cm(2) indicate a high asymmetrical and covalent environment in the optical glasses. The spontaneous emission probabilities A(ij) corresponding to the 1D2→3H4, 3P0→3H6, and 3P0→3F2 transitions are derived to be 1859.6, 6270.1 and 17276.3s(-1), respectively, and the relevant stimulated emission cross-sections σ(em) are 5.20 × 10(-21), 14.14 × 10(-21) and 126.77 × 10(-21)cm(2), confirming that the effectiveness of the red luminescence in Pr3+-doped NZPGT glasses. Under the commercial blue LED excitation, the radiant flux and the quantum yield for the red fluorescence of Pr3+ are solved to be 219μW and 11.80%, respectively. 85.24% photons of the fluorescence in the visible region are demonstrated to be located in 600-720nm wavelength range, which matches the excitation band of the most photosensitizers (PS), holding great promise for photodynamic therapy (PDT) treatment and clinical trials.

Lower extremity radicular pain after prophylactic intrathecal saline injection through a subarachnoid catheter following accidental dural puncture

We describe a case in which severe lower extremity radicular pain occurred after administration of 0.9% saline into the subarachnoid space through a catheter that had been left for 20 h following inadvertent dural puncture in an obstetric patient. A 42-year-old (G8P7) woman was admitted for repeat cesarean delivery. Accidental dural puncture occurred during epidural placement. Following a slow 10-mL intrathecal injection of 0.9% normal saline an epidural catheter was advanced into the subarachnoid space. Spinal anesthesia was used for cesarean delivery and the subarachnoid catheter was kept in place for 20 h. Before catheter removal, an additional 10 mL of 0.9% saline was slowly administered into the intrathecal space. Almost instantly, the patient complained of back pain that progressed to lower extremity radicular pain and paresthesia; symptoms began to resolve after 10 min. Subsequently, the patient developed a postdural puncture headache that persisted for three days. The patient's radiculitis and paresthesia likely resulted from an acute increase in intrathecal pressure after saline administration or from direct catheter irritation. Although both intrathecal saline administration and subarachnoid catheter placement have been previously proposed as ways to prevent postdural puncture headache, their efficacy remains controversial, and we advise caution with these techniques.

Biodegradation of organic compounds from coking wastewater with UASB reactor

The UASB reactor was applied for biodegradation of organic compounds in coking wastewater. The influent pH ranged between 6.8 and 7.2, and stirring speed and temperature were controlled at 2 r/min and 30±1°C, respectively. The reactor was successfully started up in 133 days. When the influent COD was 2,600 mg/L (VLR was 2.6 kg/m(3) d), the removal rate of COD was about 54% and the effluent VFA was below 400 mg/L. GC/MS analysis indicated that the coking wastewater mainly contained aniline, phenol, o-phenol, p-cresol, benzoic acid, indole, quinoline etc. Twenty four kinds of organic compounds were detected in the influent, and 20 kinds of organic compounds were completely removed in the UASB reactor. The biodegradation of organic compounds followed Grau second-order kinetics. It was proved to be an effective and feasible method for coking wastewater anaerobic treatment.

Selective elimination of alloreactivity from immunotherapeutic T cells by photodynamic cell purging and memory T-cell sorting

Allogeneic stem cell transplantation (alloSCT), especially in the mismatched setting, carries a high risk of life-threatening GvHD because of activation of donor T cells by Ag present on host cells. Removal of mature donor T cells can prevent GvHD but leads to delayed immune reconstitution, and an increased incidence of opportunistic infections and disease relapse. These findings demonstrate the vital role of donor T cells in providing graft-versus-tumor (GvT) and anti-pathogen effects as well as facilitating immune reconstitution. It has been well documented that GvHD can be separated from GvT effects, making it possible potentially to eliminate GvHD while preserving the immunotherapeutic benefits of donor T cells. Over the past decade, major attempts have been made to reduce GvHD incidence without loss of GvT effect, especially in the haplo-identical setting. Novel techniques to deplete host-reactive donor T cells selectively have been explored. This review focuses on the use of the photodynamic cell purging (PDP) process and of sorting memory T cells for the selective elimination of alloreactivity. Minimizing the threat of GvHD while maximizing the beneficial GvT effect would broaden the scope and effectiveness of alloSCT.

A survey of microbial contamination of food contact surfaces at broiler slaughter plants in Taiwan

Microbial contamination levels at broiler slaughter plants were investigated at three major slaughter plants in Taiwan during the summer and winter. The microbial contamination levels in chicken carcasses and on food contact surfaces were examined using the swab method. The results indicated that the bacterial counts were affected by the slaughter processing plant, processes, and season (P < 0.05). The bacterial counts on food contact surfaces of the equipment before operation were not significantly lower than those after processing. Regardless of the bacterial type, bacterial counts of chicken carcasses generally decreased from the scalding step to the washing step before evisceration and then increased. The cleaning procedures for food contact surfaces should be evaluated, and special attention should be given to utensils used during processing, such as gloves, baskets, and hand tools.

T-Cell recovery in adults and children following umbilical cord blood transplantation

T-cell reconstitution following allogeneic stem cell transplantation may involve thymic education of donor-derived precursors or peripheral expansion of mature T cells transferred in the graft. T cell-receptor excision circles (sjTRECs) are generated within the thymus and identify new thymic emigrants and those that have not divided. We measured quantitative and qualitative immunologic reconstitution and sjTREC levels in adult and pediatric recipients of umbilical cord blood transplants (UCBTs). sjTRECs were detected at normal levels in all children, starting 12 months after transplantation. sjTRECs were not detected until 18 months after transplantation in adults, and then only at a 3-fold lower level than expected for age. We used complementarity-determining region 3 (CDR3) spectratyping to measure changes in T cell-receptor diversity occurring with restoration of thymic function. T-cell repertoires were skewed in adults and children at 12 to 18 months after transplantation but recovered to near-normal diversity at 2 to 3 years post-UCBT. T-cell repertoires appeared more diverse earlier in children (at 1 to 2 years post-UCBT) than in adults (at 3 to 4 years post-UCBT). We conclude that early T-cell recovery after UCBT occurs primarily through peripheral expansion of adoptively transferred donor T cells and results in skewing of the T-cell repertoire. The reappearance of sjTREC-containing cells after UCBT is associated with increasing numbers of phenotypicaly naive T cells, improved mitogen and recall antigen responses, and diversification of the T-cell repertoire. The delay in central T-cell recovery in adults relative to children may be due to differences in thymic function resulting from age-related atrophy, graft-versus-host disease, or the pharmacologic effects of prophylaxis and treatment of graft-versus-host disease.

Twenty-one-gauge needles provide more cellular samples than twenty-five-gauge needles in fine-needle aspiration biopsy of the thyroid but may not provide increased diagnostic accuracy

The technique of fine-needle aspiration (FNA) biopsy of the thyroid is important to evaluate malignancy in thyroid nodules. Eighty-five percent of thyroid FNA procedures lead to sufficient cellular material for diagnosis. With more cells aspirated, the chance of sufficiency for diagnosis increases. Large-bore needles lead to more cellular material being aspirated but bloodier specimens that may interfere with cytologic interpretation. Small-bore needles may result in too few cells for diagnosis. We conducted a randomized prospective study contrasting 21-gauge and 25-gauge needles in the evaluation of 50 consecutively enrolled nodules at our institution. In our investigation, 21-gauge needles more frequently provided superior biopsy specimens (50%) than did 25-gauge needles (18%). In the remaining specimens (32%), the 21-gauge and 25-gauge needles provided similar cellular material. The rate of sufficient samples was the same. We conclude that use of 21-gauge needles results in more cellular specimens but may not result in increased diagnostic accuracy.

[Repair and reconstruction of massively damaged wounds]

OBJECTIVE

To report repair and reconstruction of massively damaged wound under unusual condition.

METHODS

One hundred and forty-seven patients with deep tissue defects were admitted from January 1993 to December 2000, among them, 96 cases suffered from electrical injury, 18 cases with hot press injury, 18 cases with deep burns as a result of CO poisoning or epileptic seizure, 6 cases caused by chemical producing necrosis and wound infection, 3 cases with radiation injuries, 2 cases with chemical burn, 2 cases with explosive injury, 2 cases with frostbite. One hundred and seventy five wounds in 147 patients were repaired by transfer of local flap, forearm conversal island skin flap, pectoralis major myocutaneous flap, delto-pectoral skin flap, latissimus dorsi skin flap, gastroecnemius myocutaneous flap, anterior and posterior tibial artery island skin flap, and so on. The wound defect ranged from 1 cm x 1 cm to 20 cm x 28 cm, and the flaps were 1.5 cm x 2.0 cm to 22 cm x 30 cm. The necrotic tendon was replaced with acellular allogenic tendon simultaneously in 7 cases.

RESULTS

One hundred and sixty-nine flaps were survival with first intention, while necrosis of the tip of flap occurred in 6 cases. The transplantation of acellular allogenic tendon in all cases were survival. The function and configuration in 28 cases were satisfactory after 4 months to 8 years follow-up.

CONCLUSION

Various types of flaps are choosen according to the position, defect range and degree of wound, which is an ideal method to restore the function and to improve patients' living condition.

Triptolide, a novel immunosuppressive and anti-inflammatory agent purified from a Chinese herb Tripterygium wilfordii Hook F

Triptolide is a diterpenoid triepoxide purified from a Chinese herb Tripterygium Wilfordii Hook F (TWHF). TWHF has been used in traditional Chinese medicine for more than two thousand years. However, its potential value was recognized by the western medicine only after investigators observed the effectiveness of TWHF in the treatment of leprosy and rheumatoid arthritis. Triptolide has been identified as the major component responsible for the immunosuppressive and anti-inflammatory effects of TWHF. Triptolide inhibits both Ca(2+)-dependent and Ca(2+)-independent pathways and affects T cell activation through inhibition of interleukin-2 transcription at a site different from the target of cyclosporin A. Triptolide also has inhibitory effects on a variety of proinflammatory cytokines and mediators and on the expression of adhesion molecules by endothelial cells. Triptolide is effective for the treatment of a variety of autoimmune diseases and in prevention of allograft rejection and graft-versus-host disease in both animals and humans. Moreover, triptolide possesses antitumor and male anti-fertility effect. However, the toxicities of triptolide may be associated with renal, cardiac, hematopoietic and reproductive systems. Currently available data suggest that triptolide is a promising immunosuppressive and anti-inflammatory agent and should be explored further in autoimmune diseases and transplantation.

Graft-versus-host disease prevention by rapamycin: cellular mechanisms

Understanding the cellular mechanisms that lead to graft-versus-host disease (GVHD) may lead to alternative approaches in the prevention or therapy of this disease process. In this manuscript, we investigated the mechanisms of action of the immunosuppressive drug rapamycin for the prevention of GVHD. GVHD-free long-term survival was achieved in BALB/c (H2d, Mls-2a, Mls-3a) recipients of B10.D2/nSnJ (H-2d, Mls-2a, Mls-3a) bone marrow and spleen cells after a 30-day course of high-dose rapamycin (5 mg/kg per day). Low responses to recipient and third-party cells in a mixed lymphocyte reaction (MLR) were observed as well as decreased mature T-cell numbers in the spleen. This low response was not due to defective interleukin (IL)-2 production, because exogenous IL-2 did not improve the responses in the MLR. However, GVHD-free long-term survival was associated with a large number of infiltrating mononuclear cells in the target organs of GVHD. This observation suggested the possibility that these cells were responsible for suppressing the immune response. Regulatory cells, which could suppress both antirecipient and third-party responses in vitro, were demonstrated to be present in the spleens of these GVHD-free long-term survivors. These results suggest that in addition to impaired cellular immune function, the presence of non-specific regulatory cells (ie, suppression) may contribute to maintenance of GVHD-free long-term survival induced by short-course rapamycin.

Effects of aflatoxin and carotenoids on growth performance and immune response in mule ducklings

The purpose of this study was to investigate if carotenoids could alleviate the adverse effects caused by aflatoxin with respect to growth performance and immune response. In two experiments, a total of 320 mule ducklings were assigned to 5 treatments, i.e. control, aflatoxin B(1) (AFB(1)) 200 ppb, AFB(1) +beta-carotene (BC) 200 ppm, AFB(1)+BC 400 ppm, and AFB(1)+astaxanthin (AS) 200 ppm. In experiment 1, the addition of beta-carotene or astaxanthin in the diet containing AFB(1) 200 ppb resulted in a significant decrease in average daily gain as compared with the control. AFB(1) 200 ppb alone and the addition of BC or AS on top of AFB(1) resulted in a significantly lower daily feed intake than for the control group. There were no significant differences in relative organ weights among treatment groups. Both treatments of BC 400 ppm and AS 200 ppm had significantly more macrophages harvested per duck than the control and AFB(1) 200 ppb treatments. However, there were no significant differences among treatments in percentages of phagocytotic macrophages and number of Candida albican phagocytized by phagocytotic macrophages. In experiment 2, blood biochemical parameters and antibody titers were evaluated. There were no significant differences among treatments in total bilirubin content and alkaline phosphatase activity in the serum or in antibody titers against fowl cholera. However, AFB(1) treatment had the highest activities of AST and ALT in the serum. The addition of BC 400 ppm on top of AFB(1) significantly reduced ALT activity as compared with the AFB(1) 200 ppb treatment. These results suggest that carotenoids could provide a slightly toxic alleviating effect on growth performance, enhance the chemotaxis ability of macrophages, and reduce ALT activity elevated by AFB(1).

Prevention of graft-versus-host disease by a novel immunosuppressant, PG490-88, through inhibition of alloreactive T cell expansion

BACKGROUND

PG490-88 is a water soluble, semisynthetic derivative of a novel compound PG490 (triptolide) purified from the Chinese herb Tripterygium Wilfordii Hook F.

METHODS

PG490-88 was administrated into recipient mice in a model (B10.D2-->BALB/c) of lethal graft-versus-host disease (GVHD) to study the effects of PG490-88 on GVHD and on the various steps involved in the pathological course of GVHD.

RESULTS

Injection of PG490-88 i.p. at a dose of 0.535 mg/kg/day for the first 3 weeks after transplantation protected all the recipients from developing GVHD up to 100 days after transplantation. PG490-88 inhibited in vivo both CD4+Vbeta3+ and CD8+Vbeta3+ T cell (alloreactive T cells in this model) expansion in the spleen by 64.09 and 34.02%, respectively, at the time when Vbeta3+ cell expansion was in the logarithmic phase (day 3 after transplantation). Intracellular cytokine staining without further in vitro activation demonstrated 47.42% inhibition of IL-2 production among CD4+ spleen cells in PG490-88-treated mice as compared to GVHD control on day 3 after transplantation. In contrast, CD25 (alpha chain of interleukin-2 receptor) expression did not differ.

CONCLUSIONS

PG490-88 is highly effective in prevention of murine GVHD. The immunosuppressive effect of PG490-88 is mediated by inhibition of alloreactive T cell expansion through interleukin-2 production.

Chromium-induced glucose uptake, superoxide anion production, and phagocytosis in cultured pulmonary alveolar macrophages of weanling pigs

The dose-dependent effects of chromium chloride (CrCl3) and chromium picolinate (CrPic) were evaluated for their glucose uptake, superoxide anion (O2-) production, activity of glucose-6-phosphate dehydrogenase, and phagocytosis of incubated pulmonary alveolar macrophages in medium containing no or 5 x 10(-8)M insulin. Glucose uptake was found to increase in cells treated with 20 microg/L CrCl3. Incubation with 20 microg/L of CrPic enhanced glucose uptake and O2- production in an insulin-dependent manner. However, the inclusion of CrPic to 100 microg/L in the medium absent of insulin also increased O2- production. The activity of glucose-6-phosphate dehydrogenase was not affected by either the addition of Cr or insulin. The phagocytosis of Escherichia coli by macrophages was enhanced significantly (p < 0.05) in medium containing 10-100 microg/L CrCl3 or 20-100 microg/L CrPic in the presence of insulin. These results suggest that the addition of 10-20 microg/L CrCl3 enhances directly the cellular activity of macrophages, whereas the effect of CrPic requires the cooperative action of insulin in enhancing their glucose uptake and phagocytosis.

Managing an animal health emergency in Taipei China: foot and mouth disease

Taipei China had been free from foot and mouth disease (FMD) over 68 years before the disease occurred in March 1997. The first suspected case was recorded on a pig farm in the Hsinchu Prefecture on 14 March 1997. Based on clinical signs, gross histopathological findings, and results of enzyme-linked immunosorbent assays and reverse-transcriptase polymerase chain reaction tests, diagnosis of FMD was confirmed by the Taiwan Animal Health Research Institute on 19 March 1997 and was reconfirmed by the FMD World Reference Laboratory in Pirbright (United Kingdom), on 25 March 1997. By the end of July 1997, 6,147 pig farms (about a quarter of the pig farms in Taipei China), were affected. The disease was well under control within two months by means of stamping-out and blanket vaccination. The Government purchased 21 million doses of inactivated oil-adjuvant FMD vaccine, which allowed for two injections per pig and one injection of other cloven-hoofed animals. Before the vaccine was used, the stamping-out policy was implemented, ensuring that all pigs in the affected farms were destroyed. After blanket vaccination, a partial stamping-out policy was adopted, i.e. only pigs showing clinical signs were destroyed.

Fresh vs aged benzylpenicillin on non-IgE responses in mice

AIM

To study whether or not the freshly prepared benzylpenicillin could induce different non-IgE antibody response from aged benzylpenicillin.

METHODS

Antibody response was determined by enzyme-linked immunosorbent assay (ELISA). Antigen molecules recognized by antibodies and antigenic cross reactions were tested by hapten inhibition assay.

RESULTS

Isotypes of specific non-IgE antibodies induced by freshly prepared benzylpenicillin were mainly IgM, and then IgG and IgA. Some parts of specific antibodies recognized benzylpenicillin molecule and major parts combined with degraded or transforming products. Isotypes of antibodies responsible for cross reaction were mainly IgG between benzylpenicillin and ampicillin and IgM between benzylpenicillin and piperacillin.

CONCLUSION

Freshly prepared and aged benzylpenicillin induced different non-IgE antibody response.

Acute and subacute toxicity study of water-soluble polyalkylsulfonated C60 in rats

Polyalkylsulfonated C60, or FC4S, a highly water-soluble caged fullerene derivative, is believed to be a free radical remover or an antioxidant in biological systems. A 50 mg/ml aqueous solution was prepared as a master solution and administered to female Sprague-Dawley CD(Crl:CD(SD)BR) rats in a single-dose acute toxicity study or a 12-day subacute toxicity study where rats were given the solution daily. In a study of the median lethal dose (LD50), no rats died after oral administration, and thus FC4S was considered to be nontoxic if administered orally. In an LD50 intraperitoneal injection study, rats died within 30 hr after injection; the LD50 was determined to be approximately 600 mg per kilogram of body weight. Rats injected with the compound intraperitoneally or intravenously immediately eliminated the compound through the kidney; the kidney appeared to be the primary target organ. The compound induced a distinct lysosome-overload nephrosis, a phagolysosomal nephropathy characterized by a tinctorial difference between the outer cortex and the inner cortex and the medulla. The affected outer cortex showed a diffuse degeneration, with the presence of numerous large vacuoles and cytoplasmic aggregates in the tubular epithelium. The phagolysosomal nephropathy was detected in rats after acute exposure as well as in the surviving rats following 1 intraperitoneal injection of 500 mg/kg or intravenous injection of 100 mg/kg. Ultrastructural investigation revealed numerous membranous conglomerates characteristic of phagolysosomal and/or lysosomal inclusions in the cytoplasm of the renal tubular epithelium. These conglomerates were confined to the vacuole, electron-dense, and unevenly stained. They varied in size and shape and were fused or aggregated. Occasional phagolysosomes were also observed in the endothelial cells of the peritubular plexus. A preliminary study of microsomal enzyme activity analysis revealed a suppression effect of liver cytochrome P-450-dependent monooxygenase activities, including cytochrome P-450, cytochrome b5, and benzo(a)pyrene hydroxylase, but an increased level of kidney cytochrome P-450-dependent monooxygenase activities, including NADPH-cytochrome P-450 reductase. The significance of these enzyme alterations was not well determined. Further study is needed to clarify the correlation between the alterations of microsomal enzyme activity and the nephropathy of lysosomal overload-induced changes. These changes may serve as a biological marker in toxicity screening tests for this class of compound.

A noninvasive method in the differential diagnosis of vecuronium-induced and magnesium-induced protracted neuromuscular block in a severely preeclamptic patient

The occurrence of neuromuscular blockade and the resulting potentiation of muscle relaxants during magnesium sulfate (MgSO4) administration is well known. However, a method to differentiate the neuromuscular block induced by magnesium from that induced by curariform nondepolarizing muscle relaxant in the clinical setting has never been reported. We report a case in which the duration of action of 1 mg of vecuronium lasted 4 hours in a patient with severe preeclampsia whose serum magnesium level was in the therapeutic range. We believe this is a remarkable potentiation on record in the literature. We also describe a new, noninvasive method to assess magnesium-induced neuromuscular block when curariform muscle relaxant was given simultaneously.

Circulating clonal lymphocytes in myeloma constitute a minor subpopulation of B cells

The mononuclear cells in the blood of myeloma patients have been reported to contain a high proportion of phenotypically abnormal myeloma B lymphocytes. These cells have been proposed to constitute the drug-resistant proliferative myeloma cell compartment. To determine the extent of B lymphocyte involvement, the proportion of clonotypic cells among the CD19-expressing cells from myeloma patients was estimated by quantitative polymerase chain reaction analysis of the third complementarity determining region (CDR3). The results indicate that the B lymphocytes constitute, on average, 6% of blood mononuclear cells, and that only a minor fraction of these are clonally related to the myeloma cells. While the small number of circulating clonal cells is not incompatible with their proposed role as a reservoir of proliferating myeloma progenitors, the majority of the B cells appear not to be clonally related to the myeloma cells.

Suppression of Escherichia coli alkB mutants by Saccharomyces cerevisiae genes

The alkB gene is one of a group of alkylation-inducible genes in Escherichia coli, and its product protects cells from SN2-type alkylating agents such as methyl methanesulfonate (MMS). However, the precise biochemical function of the AlkB protein remains unknown. Here, we describe the cloning, sequencing, and characterization of three Saccharomyces cerevisiae genes (YFW1, YFW12, and YFW16) that functionally complement E. coli alkB mutant cells. DNA sequence analysis showed that none of the three gene products have any amino acid sequence homology with the AlkB protein. The YFW1 and YFW12 proteins are highly serine and threonine rich, and YFW1 contains a stretch of 28 hydrophobic residues, indicating that it may be a membrane protein. The YFW16 gene turned out to be allelic with the S. cerevisiae STE11 gene. STE11 is a protein kinase known to be involved in pheromone signal transduction in S. cerevisiae; however, the kinase activity is not required for MMS resistance because mutant STE11 proteins lacking kinase activity could still complement E. coli alkB mutants. Despite the fact that YFW1, YFW12, and YFW16/STE11 each confer substantial MMS resistance upon E. coli alkB cells, S. cerevisiae null mutants for each gene were not MMS sensitive. Whether these three genes provide alkylation resistance in E. coli via an alkB-like mechanism remains to be determined, but protection appears to be specific for AlkB-deficient E. coli because none of the genes protect other alkylation-sensitive E. coli strains from killing by MMS.

The Escherichia coli AlkB protein protects human cells against alkylation-induced toxicity

Escherichia coli can ameliorate the toxic effects of alkylating agents either by preventing DNA alkylation or by repairing DNA alkylation damage. The alkylation-sensitive phenotype of E. coli alkB mutants marks the alkB pathway as an extremely effective defense mechanism against the cytotoxic effects of the SN2, but not the SN1, alkylating agents. Although it is clear that AlkB helps cells to better handle alkylated DNA, no DNA alkylation repair function could be assigned to the purified AlkB protein, suggesting that AlkB either acts as part of a complex or acts to regulate the expression of other genes whose products are directly responsible for alkylation resistance. However, here we present evidence that the provision of alkylation resistance is an intrinsic function of the AlkB protein per se. We expressed the E. coli AlkB protein in two human cell lines and found that it confers the same characteristic alkylation-resistant phenotype in this foreign environment as it does in E. coli. AlkB expression rendered human cells extremely resistant to cell killing by the SN2 but not the SN1 alkylating agents but did not affect the ability of dimethyl sulfate (an SN2 agent) to alkylate the genome. We infer that SN2 agents produce a class of DNA damage that is not efficiently produced by SN1 agents and that AlkB somehow prevents this damage from killing the cell.