Use of microsphere technology for targeted delivery of rifampin to Mycobacterium tuberculosis-infected macrophages

Microsphere technology was used to develop formulations of rifampin for targeted delivery to host macrophages. These formulations were prepared by using biocompatible polymeric excipients of lactide and glycolide copolymers. Release characteristics were examined in vitro and also in two monocytic cell lines, the murine J774 and the human Mono Mac 6 cell lines. Bioassay assessment of cell culture supernatants from monocyte cell lines showed release of bioactive rifampin during a 7-day experimental period. Treatment of Mycobacterium tuberculosis H37Rv-infected monocyte cell lines with rifampin-loaded microspheres resulted in a significant decrease in numbers of CFU at 7 days following initial infection, even though only 8% of the microsphere-loaded rifampin was released. The levels of rifampin released from microsphere formulations within monocytes were more effective at reducing M. tuberculosis intracellular growth than equivalent doses of rifampin given as a free drug. These results demonstrate that rifampin-loaded microspheres can be formulated for effective sustained and targeted delivery to host macrophages.

Peptidoglycolipid nature of the superficial cell wall sheath of smooth-colony-forming mycobacteria

The most superficial cell wall layer present in smooth-colony-forming mycobacteria was isolated from serovar 20 of the Mycobacterium avium-Mycobacterium intracellulare-Mycobacterium scrofulaceum (MAIS) serocomplex and examined chemically and by electron microscopy. Most (70 to 80%) of the fibrillar material consisted of an array of serologically active, acetylated C-myosidic peptidoglycoplipids with the basic structure (formula, see text) but in which the location of acetyl groups and the arrangement of monosaccharides have not been defined. Apparently, all serovars within the MAIS complex are characterized by structurally related superficies in which the monoglycosyl-lipopeptide portion is invariable but the oligosaccharide attachment is peculiar to each serovar. These unique inert structures may be an important factor in shielding the pathogen within phagolysosomes from lysosomal enzymes.

Isolation in high frequency of rough variants of Mycobacterium intracellulare lacking C-mycoside glycopeptidolipid antigens

Rough variants of serovars from the Mycobacterium avium-Mycobacterium intracellulare-Mycobacterium scrofulaceum complex were isolated in high frequency from pellicle growth of the wild-type strains. Rough morphology could be correlated with the lack of an outer cell wall sheath and its constituent C-mycoside glycopeptidolipids of both the serologically active and inactive types.

Synergistic activities of antituberculous drugs with cerulenin and trans-cinnamic acid against Mycobacterium tuberculosis

The recent upsurge in the incidence of tuberculosis with significant emergence of multidrug-resistant cases has focused on the priority of discovering effective new drugs and on the strategies to augment the potential of existing drugs against Mycobacterium tuberculosis. In the present study, we investigated cerulenin and trans-cinnamic acid, which have recently been shown to augment the activity of various antibiotics against Mycobacterium avium [Antimicrob. Agents Chemother. 38 (1994) 2287-2295], to enhance the activity of isoniazid, rifampin, ofloxacin, amikacin and clofazimine against M. tuberculosis. The synergy observed was compared with identical combinations using ethambutol, a cell wall-inhibiting drug used in standard antituberculous chemotherapy. The results showed that ethambutol resulted in synergistic activity in 12/30 drug combinations, as compared to 15/36 for cerulenin and 101/18 for trans-cinnamic acid. This increase in drug activity was even observed with drug-resistant isolates. Use of novel antimicrobials and understanding of their mechanisms of action may be an effective strategy to determine previously undescribed targets for future drug development.

Anti-HIV natural product (+)-calanolide A is active against both drug-susceptible and drug-resistant strains of Mycobacterium tuberculosis

Naturally occurring anti-HIV-1 agent (+)-calanolide A was found to be active against all of the strains of Mycobacterium tuberculosis tested, including those resistant to the standard antitubercular drugs. Efficacy evaluations in macrophages revealed that (+)-calanolide A significantly inhibited intracellular replication of M. tuberculosis H37Rv at concentrations below the MIC observed in vitro. Preliminary mechanistic studies indicated that (+)-calanolide A rapidly inhibits RNA and DNA synthesis followed by an inhibition of protein synthesis. Compared with known inhibitors, this scenario is more similar to effects observed with rifampin, an inhibitor of RNA synthesis. Since (+)-calanolide A was active against a rifampin-resistant strain, it is believed that these two agents may involve different targets. (+)-Calanolide A and its related pyranocoumarins are the first class of compounds identified to possess antimycobacterial and antiretroviral activities, representing a new pharmacophore for anti-TB activity.

Antimycobacterial activities of 2,4-diamino-5-deazapteridine derivatives and effects on mycobacterial dihydrofolate reductase

Development of new antimycobacterial agents for Mycobacterium avium complex (MAC) infections is important particularly for persons coinfected with human immunodeficiency virus. The objectives of this study were to evaluate the in vitro activity of 2, 4-diamino-5-methyl-5-deazapteridines (DMDPs) against MAC and to assess their activities against MAC dihydrofolate reductase recombinant enzyme (rDHFR). Seventy-seven DMDP derivatives were evaluated initially for in vitro activity against one to three strains of MAC (NJ168, NJ211, and/or NJ3404). MICs were determined with 10-fold dilutions of drug and a colorimetric (Alamar Blue) microdilution broth assay. MAC rDHFR 50% inhibitory concentrations versus those of human rDHFR were also determined. Substitutions at position 5 of the pteridine moiety included -CH(3), -CH(2)CH(3), and -CH(2)OCH(3) groups. Additionally, different substituted and unsubstituted aryl groups were linked at position 6 through a two-atom bridge of either -CH(2)NH, -CH(2)N(CH(3)), -CH(2)CH(2), or -CH(2)S. All but 4 of the 77 derivatives were active against MAC NJ168 at concentrations of < or =13 microg/ml. Depending on the MAC strain used, 81 to 87% had MICs of < or =1.3 microg/ml. Twenty-one derivatives were >100-fold more active against MAC rDHFR than against human rDHFR. In general, selectivity was dependent on the composition of the two-atom bridge at position 6 and the attached aryl group with substitutions at the 2' and 5' positions on the phenyl ring. Using this assessment, a rational synthetic approach was implemented that resulted in a DMDP derivative that had significant intracellular activity against a MAC-infected Mono Mac 6 monocytic cell line. These results demonstrate that it is possible to synthesize pteridine derivatives that have selective activity against MAC.

Postphagocytic detection of glycopeptidolipids associated with the superficial L1 layer of Mycobacterium intracellulare

The superficial L1 layer of Mycobacterium intracellulare serovar 20 was detected by immunocytochemical procedures based on C-mycoside glycopeptidolipid (GPL) antigens. Specific immune serum was produced by injecting a GPL-methylated bovine serum albumin complex into rabbits with Freund incomplete adjuvant. The resulting antibodies were used to label serovar 20 with goat anti-rabbit immunoglobulin G (IgG) conjugated with either fluorescein or ferritin. The labeled GPL antigens were then detected by fluorescent and electron microscopy. With these procedures, it was possible to observe the superficial distribution of the GPL antigens on serovar 20 and to confirm their intraphagosomal location within the macrophages after phagocytosis. These immunocytochemical procedures now make it possible to monitor these mycobacterial antigens during phagocytosis and may be helpful in determining their role in pathogenesis.

Susceptibilities of Mycobacterium tuberculosis and Mycobacterium avium complex to lipophilic deazapteridine derivatives, inhibitors of dihydrofolate reductase

Twelve lipophilic 2,4-diamino-5-methyl-5-deazapteridine derivatives and trimethoprim were evaluated for activity against Mycobacterium tuberculosis and Mycobacterium avium in vitro. Six of the compounds had MICs of < or =12.8 mg/L and < or =1.28 mg/L against M. tuberculosis and M. avium, respectively; trimethoprim MICs were >128 mg/L and >12.8 but < or =128 mg/L, respectively. Two compounds, with either a 2-methyl-5-methoxy phenyl or 2-methoxy-5-trifluoromethyl phenyl linked at the 6-position of the deazapteridine moiety by a CH2NH bridge, had MICs of < or =0.13 mg/L against M. avium; the two compounds also had apparent I50 values for dihydrofolate reductase of 2 and 8 nM, respectively, compared with an I50 of 400 nM with trimethoprim. Four of the compounds were selectively toxic to mycobacteria as compared with Vero cells. These results demonstrated that lipophilic antifolates can be synthesized which are more active against mycobacteria than trimethoprim and which possess selective toxicity.

Immunomodulatory spectrum of lipids associated with Mycobacterium avium serovar 8

Lipid fractions obtained from Mycobacterium avium serovar 8 were assessed for the ability to affect various immune functions of human peripheral blood mononuclear cells (PBM). Lipids included a total lipid fraction and fractions eluted from silicic acid column separation of that total lipid fraction, using chloroform and chloroform-methanol combinations. Lipid fractions were assayed for total carbohydrate and total 6-deoxyhexose content and were assessed for the ability to influence human macrophage function and the capacity to induce secretion of prostaglandin E2 (PGE2) and tumor necrosis factor alpha in PBM. The total lipid and serovar-specific glycopeptidolipid (GPL) fractions both induced significant levels of tumor necrosis factor alpha, as well as PGE2, in PBM exposed to a sublethal concentration of 100 micrograms lipid per 2 x 10(6) cells. In addition, the same concentrations of the 5 to 7% and GPL fractions induced significant levels of leukotriene B4 in PBM. Comparison of carbohydrate and 6-deoxyhexose contents of each fraction suggested a relationship to carbohydrate content and ability of fractions to induce immune modulator secretion. Analysis of GPL fractions from M. avium serovars 4 and 20 revealed that those GPL lacked the ability to induce PGE2. These results are explained by considering the difference in the carbohydrate residues of the oligosaccharide moieties.

Crystal structure of Bacillus anthracis dihydrofolate reductase with the dihydrophthalazine-based trimethoprim derivative RAB1 provides a structural explanation of potency and selectivity

Bacillus anthracis possesses an innate resistance to the antibiotic trimethoprim due to poor binding to dihydrofolate reductase (DHFR); currently, there are no commercial antibacterials that target this enzyme in B. anthracis. We have previously reported a series of dihydrophthalazine-based trimethoprim derivatives that are inhibitors for this target. In the present work, we have synthesized one compound (RAB1) displaying favorable 50% inhibitory concentration (54 nM) and MIC (< or =12.8 microg/ml) values. RAB1 was cocrystallized with the B. anthracis DHFR in the space group P2(1)2(1)2(1), and X-ray diffraction data were collected to a 2.3-A resolution. Binding of RAB1 causes a conformational change of the side chain of Arg58 and Met37 to accommodate the dihydrophthalazine moiety. Unlike the natural substrate or trimethoprim, the dihydrophthalazine group provides a large hydrophobic anchor that embeds within the DHFR active site and accounts for its selective inhibitory activity against B. anthracis.

Immunomodulation of human peripheral blood mononuclear cell functions by defined lipid fractions of Mycobacterium avium

Mycobacterial fractions, some of which are associated with the cell envelope of Mycobacterium avium serovar 4, were assessed for their ability to affect various immunological functions of human peripheral blood mononuclear cells (PBM). Treatment of PBM with a total lipid fraction derived from M. avium serovar 4 resulted in a significant suppression of lymphoproliferative responsiveness to phytohemagglutinin stimulation at concentrations not affecting cell viability. Although a similar suppression was not observed when PBM were treated with purified serovar 4-specific glycopeptidolipids (GPL), treatment with the beta-lipid fragment derived from the GPL did result in a significant suppression of phytohemagglutinin responsiveness. Further studies revealed that the total lipid fraction and the beta-lipid fragment were effective at significantly reducing the ability of human macrophages to restrict the intracellular growth of mycobacteria and at stimulating PBM to secrete prostaglandin E2. These same effects were not observed when purified GPL or the reduced oligosaccharide fragment of the GPL was used. Other studies revealed that the total lipid and purified GPL fractions were effective at stimulating tumor necrosis factor alpha release from human PBM, whereas the beta-lipid fragment was not. These results indicate that mycobacterial lipids have various immunomodulatory capabilities, depending upon their chemical nature and ability to interact with certain host cells.

Modified lymphocyte response to mitogens after intraperitoneal injection of glycopeptidolipid antigens from Mycobacterium avium complex

Intraperitoneal injection of glycopeptidolipid (GPL) antigens from Mycobacterium avium complex serovar 4 resulted in the decreased ability of murine splenic lymphocytes to respond to nonspecific-mitogen-induced blastogenesis when exposed to concanavalin A, phytohemagglutinin, and lipopolysaccharide. Adherent cell depletion and cell mixing experiments with T lymphocytes indicated that macrophages were not a major contributor to the immunosuppression observed in this study. Enumeration of splenic lymphocytes by means of flow-cytometry with fluorescein isothiocyanate-conjugated monoclonal antibodies demonstrated that intraperitoneal injection of GPL antigens resulted in a significant decrease in Thy-1+ and Lyt-1+ cells but no change in the numbers of Lyt-2+ cells. Treatment with GPL antigens in vitro affected the ability of splenic mononuclear cells to respond optimally for concanavalin A-induced blastogenesis at 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml and lipopolysaccharide-induced blastogenesis at concentrations ranging from 5 to 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml. However, in vitro treatment with GPL antigens did not affect phytohemagglutinin-induced blastogenesis at concentrations ranging from 5 to 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml. These findings suggest that GPL antigens or their metabolites affect lymphocyte function and may be important cofactors in the overall pathogenesis of M. avium complex infections.

Efficacy of microencapsulated rifampin in Mycobacterium tuberculosis-infected mice

Rifampin is a first-line drug useful in the treatment of tuberculosis. By using biocompatible polymeric excipients of lactide and glycolide copolymers, two microsphere formulations were developed for targeted and sustained delivery of rifampin, with minimal dosing. A small-microsphere formulation, with demonstrated ability to inhibit intracellularly replicating Mycobacterium tuberculosis H37Rv, was tested along with a large-microsphere formulation in an infected mouse model. Results revealed that by using a single treatment of the large-microsphere formulation, it was possible to achieve a significant reduction in M. tuberculosis H37Rv CFUs in the lungs of mice by 26 days postinfection. A combination of small (given as two injections on day 0 and day 7) and large (given as one injection at day 0) rifampin-loaded microsphere formulations resulted in significant reductions in CFUs in the lungs by 26 days, achieving a 1.23 log10 reduction in CFUs. By comparison, oral treatment with 5, 10, or 20 mg of rifampin/kg of body weight, administered every day, resulted in a reduction of 0.42, 1.7, or 1.8 log10 units, respectively. Thus the microsphere formulations, administered in one or two doses, were able to achieve results in mice similar to those obtained with a daily drug regimen within the range of the highest clinically tolerated dosage in humans. These results demonstrate that microsphere formulations of antimycobacterial drugs such as rifampin can be used for therapy of tuberculosis with minimal dosing.

Macrophage uptake and retention of radiolabeled glycopeptidolipid antigens associated with the superficial L1 layer of Mycobacterium intracellulare serovar 20

Glycopeptidolipid (GPL) antigens which are associated with the superficial L1 layer of Mycobacterium intracellulare serovar 20 were labeled with radioisotopes by means of internal labeling techniques and used in macrophage uptake and retention studies. The use of tritiated alanine and phenylalanine allowed the incorporation of label into the GPL invariant fatty acyl peptide core, which is common to all members of the Mycobacterium avium-M. intracellulare complex. Radiolabeled GPL antigens were then purified by a one-step column chromatographic procedure and subsequently used to determine the maximum uptake and retention in peritoneal macrophages isolated from C57BL/6 and CBA/J mice. Maximum uptake for peritoneal macrophages from both strains of mice occurred at a concentration between 200 and 250 micrograms of antigen per ml of medium when 3.4 X 10(5) cells were pulsed. Timed experiments demonstrated that approximately 20% of the antigens remained associated with the macrophages up to 4 days after a pulse of 200 micrograms of GPL, and examination of chloroform-extractable components from both macrophages and spent medium revealed that 98% or more of the radioactivity corresponded to intact GPL components. The ability of the GPL antigens to become associated with macrophages is demonstrated by these results, which strongly suggest that these potentially important mycobacterial antigens are inert to degradation by those cells.

In vitro efficacy of new antifolates against trimethoprim-resistant Bacillus anthracis

Bacillus anthracis is innately resistant to trimethoprim (TMP), a synthetic antifolate that selectively inhibits several bacterial dihydrofolate reductases (DHFRs) but not human DHFR. Previously, we were able to confirm that TMP resistance in B. anthracis (MIC > 2,048 microg/ml) is due to the lack of selectivity of TMP for the B. anthracis DHFR (E. W. Barrow, P. C. Bourne, and W. W. Barrow, Antimicrob. Agents Chemother. 48:4643-4649, 2004). In this investigation, 24 2,4-diaminopyrimidine derivatives, representing a class of compounds with dihydrophthalazine side chains, were screened for their in vitro effects on B. anthracis Sterne and their selectivities for the B. anthracis DHFR. MICs were obtained by a colorimetric (Alamar blue) broth microdilution assay. Purified human recombinant DHFR (rDHFR) and B. anthracis rDHFR were used in a validated enzyme assay to determine the 50% inhibitory concentrations (IC(50)s) and the selectivity ratios of the derivatives. The MICs ranged from 12.8 to 128 microg/ml for all but nine compounds, for which the MICs were > or =128 microg/ml. The IC(50) values for B. anthracis rDHFR ranged from 46 to 600 nM, whereas the IC(50) values for human rDHFR were >16,000 nM. This is the first report on the in vitro inhibitory actions of this class of antifolates against TMP-resistant B. anthracis isolates. The selective inhibition of B. anthracis rDHFR and the in vitro activity against B. anthracis demonstrate that members of this class of compounds have the potential to be developed into clinically important therapeutic choices for the treatment of infections caused by TMP-resistant bacteria, such as B. anthracis.

Functional cloning of Bacillus anthracis dihydrofolate reductase and confirmation of natural resistance to trimethoprim

Bacillus anthracis is reported to be naturally resistant to trimethoprim (TMP), a drug that inhibits dihydrofolate reductase (DHFR), a key enzyme in the folate pathway. A microdilution broth assay established that the MIC of TMP for B. anthracis Sterne is >2,048 but < or =4,096 microg/ml. A putative DHFR sequence was amplified from B. anthracis Sterne genomic DNA. The PCR product was cloned into the Invitrogen pCRT7/CT-TOPO vector, followed by transformation into Escherichia coli TOP10F' chemically competent cells. Plasmid DNA from a clone showing the correct construct with a thrombin cleavage site attached downstream from the terminus of the cloned PCR product was transformed into E. coli BL21 Star (DE3)pLysS competent cells for expression of the six-histidine-tagged fusion protein and purification on a His-Bind resin column. Functionality of the purified Sterne recombinant DHFR (Sterne rDHFR) was confirmed in an established enzyme assay. The 50% inhibitory concentrations of TMP and methotrexate for the Sterne rDHFR were found to be 77,233 and 12.2 nM, respectively. TMP resistance was observed with E. coli BL21 Star (DE3)pLysS competent cells transformed with the Sterne DHFR gene. Alignment of the amino acid sequence of the Sterne DHFR gene revealed 100% homology with various virulent strains of B. anthracis. These results confirm the natural resistance of B. anthracis to TMP and clarify that the resistance is correlated to a lack of selectivity for the chromosomally encoded gene product. These findings will assist in the development of narrow-spectrum antimicrobial agents for treatment of anthrax.

Antimycobacterial activity of 2-methyl-adenosine

OBJECTIVES

The aims of this study were to assess the in vitro activity of 2-methyl-adenosine against Mycobacterium tuberculosis and evaluate, and to intracellular efficacy, and to evaluate its effectiveness against M. tuberculosis in a persistent state model and examine its potential mechanism of action.

METHODS

In vitro activity was determined by means of a colorimetric microdilution broth assay. Intracellular activity was assessed with a Mono Mac 6 human monocytic cell line. A hypoxic shift-down model was used to evaluate the effect of 2-methyl-adenosine on M. tuberculosis in a persistent state. Mechanism-of-action studies were conducted by examining the effect of 2-methyl-adenosine on the uptake of appropriate radiolabelled precursors into respective mycobacterial macromolecular components.

RESULTS

Studies confirmed the in vitro activity of 2-methyl-adenosine against M. tuberculosis and demonstrated intracellular efficacy against M. tuberculosis within macrophages. 2-Methyl-adenosine was able to significantly affect the viability of M. tuberculosis in a hypoxic shift-down model previously described to simulate the persistent state that results during tuberculosis. Mechanism-of-action studies revealed that the immediate inhibitory effects of 2-methyl-adenosine were associated with protein and DNA synthesis and not RNA synthesis.

CONCLUSIONS

Results indicate that 2-methyl-adenosine, or similar derivatives, might be effective against M. tuberculosis infections during latency. This information should be helpful in understanding purine metabolism of M. tuberculosis and also the metabolic activity of this important human pathogen in the persistent state.

Modified lymphocyte response to mitogens induced by the lipopeptide fragment derived from Mycobacterium avium serovar-specific glycopeptidolipids

The beta-elimination procedure was used to obtain two major fragments of Mycobacterium avium glycopeptidolipid antigens. The lipopeptide fragment, not the oligosaccharide, diminished the mitogen-induced blastogenic response of spleen cells at concentrations lower than those which affected viability. Electron microscopy revealed an internalization of lipopeptide and disruption of intracellular organization.

Synthesis and biological activity of substituted 2,4-diaminopyrimidines that inhibit Bacillus anthracis

A series of substituted 2,4-diaminopyrimidines 1 has been prepared and evaluated for activity against Bacillus anthracis using previously reported (±)-3-{5-[(2,4-diamino-5-pyrimidinyl)methyl]-2,3-dimethoxyphenyl}-1-(1-propyl-2(1H)-phthalazinyl)-2-propen-1-one (1a), with a minimum inhibitory concentration (MIC) value of 1-3 μg/mL, as the standard. In the current work, the corresponding isobutenyl (1e) and phenyl (1h) derivatives displayed the most significant activity in terms of the lowest MICs with values of 0.5 μg/mL and 0.375-1.5 μg/mL, respectively. It is likely that the S isomers of 1 will bind the substrate-binding pocket of dihydrofolate reductase (DHFR) as in B. anthracis was found for (S)-1a. The final step in the convergent synthesis of target systems 1 from (±)-1-(1-substituted-2(1H)-phthalazinyl)-2-propen-1-ones 6 with 2,4-diamino-5-(5-iodo-3,4-dimethoxybenzyl)pyrimidine (13) was accomplished via a novel Heck coupling reaction under sealed-tube conditions.

Treatment of tuberculosis using a combination of sustained-release rifampin-loaded microspheres and oral dosing with isoniazid

Previously, we reported on the use of rifampin-loaded microspheres to effectively treat Mycobacterium tuberculosis-infected macrophages and mice. Using similar biocompatible polymeric excipients of lactide and glycolide copolymers, we have increased the rifampin loading of small microsphere formulations (1 to 10 microm) by fourfold. Improved formulations were evaluated individually and in combination with oral regimens of isoniazid for the treatment of Mycobacterium tuberculosis H37Rv-infected mice. Groups (10 mice per group) consisted of mice that received (i) oral dosages of isoniazid (25 to 0.19 mg/kg of body weight/day), (ii) two intraperitoneal injections of rifampin-loaded microspheres on days 0 and 7, (iii) a combination of small rifampin-loaded microspheres on days 0 and 7 and isoniazid orally for 25 days (12.5 to 0.39 mg/kg/day), (iv) placebo injections, and (v) no treatment. Treatment with rifampin-loaded microspheres alone resulted in significant reductions in the numbers of CFU in the lungs and spleens by day 26. A bioassay revealed that plasma rifampin levels from the microspheres exceeded the MICs by more than twofold throughout the 26-day experimental period. Susceptibility testing demonstrated continued sensitivity to rifampin during the treatment period. Whereas isoniazid alone significantly reduced the numbers of CFU for dosages ranging from 12.5 to 1.56 mg/kg, combination therapy with rifampin-loaded microspheres increased the effective range to 0.39 mg/kg. In many cases, complete elimination of CFU was obtained with the combination therapy, something not achieved with most of the single therapies. These results demonstrate the ability to use small microsphere formulations alone to achieve significant results in a murine tuberculosis model and also the ability to use them safely in combination with another antimycobacterial agent.

Use of Mono Mac 6 human monocytic cell line and J774 murine macrophage cell line in parallel antimycobacterial drug studies

The Mono Mac 6 (MM6) human monocytic cell line was evaluated with the established J774 murine macrophage cell line to ascertain its effectiveness in determining the intracellular activities of antimycobacterial drugs. Cells were infected with Mycobacterium tuberculosis H37Ra and treated with drug concentrations corresponding to the MICs, as well as to threefold higher than and threefold less than the MICs. Changes in CFU were compared after 7 days to determine significant differences between treated and nontreated groups. The results suggest that MM6 will make a useful model for testing the intracellular activities of antituberculosis drugs.

Exposure of human peripheral blood mononuclear cells to total lipids and serovar-specific glycopeptidolipids from Mycobacterium avium serovars 4 and 8 results in inhibition of TH1-type responses

Previous studies have suggested that large quantities of bacterial lipids may accumulate and persist within host cells during chronic stages of Mycobacterium avium infections. This study intended to assess the ability of purified M. avium lipids to affect TH-1-type responses in human peripheral blood mononuclear cells (PBMC) from healthy donors. PBMC were exposed to total lipids and serovar-specific glycopeptidolipids (GPL) extracted from M. avium serovars 4 and 8, which have been reported to predominate as opportunistic infection among AIDS patients. After 24 h exposure to lipids followed by PHA/PMA treatment, IL-2 and IFN-gamma were assayed in the supernatants. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for a semiquantitative estimation of mRNA for IL-2 and IFN-gamma in cell pellets at various time points. Exposure of PBMC to M. avium total lipids significantly suppressed PHA/PMA-induced secretion of IL-2 and IFN-gamma as determined by ELISA. The GPL antigens from serovar 4 were more efficient at inhibiting TH-1 responses than GPL from serovar 8. CD4(+)T-lymphocyte enrichment of PBMC demonstrated that suppression by M. avium lipids was intact without the presence of other cell populations such as monocytes and B-cells. Preliminary RT-PCR experiments showed that the secretion of TH-1 cytokines was partially affected at the transcriptional level. The results obtained showed that M. avium lipids are indeed able to modify the induction of TH-1-type cytokines by human PBMC, and suggest that accumulation of M. avium lipids in the chronic stages of infection may play an important role in the pathogenesis of HIV infection.

Comparative effects of Mycobacterium avium glycopeptidolipid and lipopeptide fragment on the function and ultrastructure of mononuclear cells

Among the various lipids associated with the cell envelope of the Mycobacterium avium complex, the species-specific glycopeptidolipids (GPL) are responsible for distinguishing one serovar from another. In a continuing effort to study the immunomodulatory capabilities of these mycobacterial lipids, we have examined and compared the effects of the GPL and its lipopeptide fragment (beta-lipid) on mononuclear cell function. It was observed that the lymphoproliferative response of murine splenic mononuclear cells to mitogen stimulation was reduced by both the GPL and its lipopeptide fragment. Although the responsiveness appeared to be down-regulated to a greater degree by the beta-lipid, treatment with either GPL or beta-lipid resulted in the release of soluble factors from peritoneal macrophages that caused suppression of the lymphoproliferative responsiveness of splenic mononuclear cells. Flow cytometric analysis of peritoneal macrophages revealed that treatment with the beta-lipid fragment caused a marked decrease in expression of the C3bi complement receptor, Mac-1, on macrophages, whereas treatment with GPL resulted in a marked increase in the expression of Mac-2 receptor on macrophages. Treatment of peritoneal macrophages with either GPL or beta-lipid resulted in the release of tumour necrosis factor (TNF), as determined by an L929 biological cytotoxicity assay. Perturbation of macrophage membrane ultrastructure by both GPL and beta-lipid was confirmed by electron microscopy, and may be a possible explanation for the resulting alterations in mononuclear cell function observed in this study.

Potential drug targets for Mycobacterium avium defined by radiometric drug-inhibitor combination techniques

Previously established radiometric techniques were used to assess the effectiveness of combined antimicrobial drug-inhibitory drug (drug-inhibitor) treatment on two clinical isolates of the Mycobacterium avium complex representing three colony variants: smooth opaque (dome) (SmO), smooth transparent (SmT), and rough (Rg). All variants were identified as members of the M. avium complex; however, only the SmT colony type of strain 373 possessed characteristic serovar-specific glycopeptidolipid (GPL) antigens. MICs, determined radiometrically, of drugs with the potential to inhibit the biosynthesis of GPL antigens or other cell envelope constituents were similar for all strains. These drugs included cerulenin, N-carbamyl-DL-phenylalanine, N-carbamyl-L-isoleucine, trans-cinnamic acid, ethambutol, 1-fluoro-1-deoxy-beta-D-glucose, 2-deoxy-D-glucose, and m-fluoro-phenylalanine. The MICs of the antimicrobial drugs amikacin, sparfloxacin, and clarithromycin varied, but overall the MICs for the SmO variant were the lowest. Radiometric assessment of drug-inhibitor combinations by using established x/y determinations revealed enhanced activity when either ethambutol or cerulenin were used in combination with all antimicrobial agents for all variants except the Rg variant of strain 424, for which ethambutol was not effective. Enhanced activity with amino acid analogs was observed with the Rg colony variants of strains 373 and 424. Two potential sites for drug targeting were identified: fatty acid synthesis, for all strains assayed, and peptide biosynthesis, particularly for Rg colony variants that possess previously identified phenylalanine-containing lipopeptides as potential targets for future drug development.

Immunogenicity of type-specific C-mycoside glycopeptidolipids of mycobacteria

Specific rabbit antibodies were obtained from the inoculation of a complex composed of methylated bovine serum albumin and the superficial type-specific C-mycoside glycopeptidolipid (GPL) antigens from serovar 20 of the Mycobacterium avium-M. intracellulare-M. scrofulaceum complex. Although the GPLs on their own are serologically active, they require the protein carrier for immunogenicity. Antibodies to the complex were detected by seroagglutination, gel diffusion, and indirect immunofluorescence. Cross-reaction was observed in the case of just one of 16 M. avium-M. intracellulare-M. scrofulaceum complex serovars tested (serovar 41). Double gel diffusion and immunoelectrophoresis showed two major antigen-antibody complexes in the reaction between anti-GPL-methylated bovine serum albumin and the GPL antigens. The studies of migration pattern and absorption indicated that immunoglobulin M was responsible for one of these complexes, whereas the antibody responsible for the second complex was unidentified. The specific anti-GPL serum is a useful tool for the identification and classification of atypical mycobacteria and for the study of the fate of the organisms and their superficies during phagocytosis.