Respiratory burst in peritoneal exudate cells in response to a modified tuftsin

Recent Developments in Drug Delivery for Treatment of Tuberculosis by Targeting Macrophages

Tuberculosis (TB) is among the greatest public health and safety concerns in the 21st century, Mycobacterium tuberculosis, which causes TB, infects alveolar macrophages and uses these cells as one of its primary sites of replication. The current TB treatment regimen, which consist of chemotherapy involving a combination of 3-4 antimicrobials for a duration of 6-12 months, is marked with significant side effects, toxicity, and poor compliance. Targeted drug delivery offers a strategy that could overcome many of the problems of current TB treatment by specifically targeting infected macrophages. Recent advances in nanotechnology and material science have opened an avenue to explore drug carriers that actively and passively target macrophages. This approach can increase the drug penetration into macrophages by using ligands on the nanocarrier that interact with specific receptors for macrophages. This review encompasses the recent development of drug carriers specifically targeting macrophages actively and passively. Future directions and challenges associated with development of effective TB treatment is also discussed.

Infection microenvironment-related antibacterial nanotherapeutic strategies

The emergence and spread of antibiotic resistance is one of the biggest challenges in public health. There is an urgent need to discover novel agents against the occurrence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The drug-resistant pathogens are able to grow and persist in infected sites, including biofilms, phagosomes, or phagolysosomes, which are more difficult to eradicate than planktonic ones and also foster the development of drug resistance. For years, various nano-antibacterial agents have been developed in the forms of antibiotic nanocarriers. Inorganic nanoparticles with intrinsic antibacterial activity and inert nanoparticles assisted by external stimuli, including heat, photon, magnetism, or sound, have also been discovered. Many of these strategies are designed to target the unique microenvironment of bacterial infections, which have shown potent antibacterial effects in vitro and in vivo. This review summarizes ongoing efforts on antibacterial nanotherapeutic strategies related to bacterial infection microenvironments, including targeted antibacterial therapy and responsive antibiotic delivery systems. Several grand challenges and future directions for the development and translation of effective nano-antibacterial agents are also discussed. The development of innovative nano-antibacterial agents could provide powerful weapons against drug-resistant bacteria in systemic or local bacterial infections in the foreseeable future.

Targeted Drug Delivery Using Tuftsin-bearing Liposomes: Implications in the Treatment of Infectious Diseases and Tumors

Tuftsin, a tetrapeptide (Thr-Lys-Pro-Arg), acts as an immunopotentiating molecule with its ability to bind and activate many immune cells, including macrophages or monocytes, neutrophils and dendritic cells. The specific targeting activity of tuftsin has been further increased by its palmitoylation followed by its incorporation into the lipid bilayer of liposomes. Tuftsin-bearing liposomes (Tuft-liposomes) possess several characteristics that enable them to act as a potential drug and vaccine carriers. Tuft-liposomes-loaded anti-microbial drugs have been shown to be highly effective against many infectious diseases, including tuberculosis, leishmaniasis, malaria, candidiasis and cryptococosis. Moreover, Tuft-liposomes also increased the activity of anticancer drug etoposide against fibrosarcoma in mice. Tuft-liposomes showed the immune-potentiating effect and rejuvenated the immune cells in the leukopenic mice. In addition, antigens encapsulated in Tuftsin-bearing liposomes demonstrated greater immunogenicity by increasing the T cell proliferation and antibody secretion. Keeping into consideration their specific targeting and immunopotentiating effects, Tuft-liposomes may potentially be used as promising drug and vaccine delivery systems.

Tuftsin-Bearing Liposomes as Antibiotic Carriers in Treatment of Macrophage Infections

Tuftsin is a tetrapeptide (Thr-Lys-Pro-Arg) that specifically binds monocytes, macrophages, and polymorphonuclear leukocytes and potentiates their natural killer activity against tumors and pathogens. The antimicrobial activity of this peptide is significantly increased by attaching at the C-terminus a fatty acyl residue through the ethylenediamine spacer arm. This activity is further augmented by incorporating the modified tuftsin in the liposomes. The tuftsin-bearing liposomes not only enhance the host's resistance against a variety of infections but also serve as useful vehicles for the site-specific delivery of drugs in a variety of macrophage-based infections, such as tuberculosis and leishmaniasis.

Immunomodulatory potential of hydrophobic analogs of Rigin and their role in providing protection against Plasmodium berghei infection in mice

Here, we report the immunomodulating potential of N-palmitoyl-amino-ethyl-rigin amide (PR) and N-cholestanyl-amino-ethyl-rigin amide (CR), the two new structural analogs of rigin (an IgG-derived tetrapeptide). Their activity profiles are compared with native tuftsin (NT) and/or N-palmitoyl-amino-ethyl-tuftsin amide (PT) taken as positive control. To explore the possibility of their use as targeting molecules, they are incorporated into the liposome bilayer and, subsequently, interacted with macrophages in an in vitro study. The new analogs of rigin with the hydrophobicity introduced at the C-terminus are found to considerably improve both the cell-mediated and the humoral immune responses in mice. However, unlike tuftsin and its analog, which mainly activate polymorphonuclear leukocytes and macrophages, the rigin analogs appear to manifest their response more through lymphocytes. When administered prophylactically to a group of mice, at the dose of 100 micrograms/0.5 ml/mouse/day for 2 days (i.v.), followed by a challenge presented with 1 x 10(6) rbcs parasitised with Plasmodium berghei on day 0, substantial reduction in parasitaemia and rate of mortality is observed. This led to increase the median survival time (MST) of the treated group in comparison to the control group. The response is found to be more prominent in CR-treated mice possibly because of the presence of steroid moiety, which is likely to have more productive interaction with cell membranes. Incorporation of these peptides into the bilayer of liposomes does not alter the permeability behavior of vesicles and, in fact, enhances their uptake by the macrophages in an in vitro study. The effect, however, is dependent on both, the concentration of peptide liposomes and the time of incubation. Present study, thus, establishes the possible use of these analogs not only as adjuvant in chemotherapy, but also as a prophylactic supplement to boost the natural immune status. The activity response of rigin analogs is manifested through lymphocytes, they can also find use in the chemotherapy of diseases, like leishmaniasis, tuberculosis and leprosy, where macrophage activity is either tamed or impaired by pathogens.

Tuftsin-bearing liposomes in treatment of macrophage-based infections

The use of liposomes as drug carriers in treatment of various diseases has been explored extensively for more than 20 years. 'Conventional' liposomes, when administered in vivo by a variety of routes, rapidly accumulate in the mononuclear phagocyte system (MPS). The inherent tendency of the liposomes to concentrate in MPS can be exploited in enhancing the non-specific host defence against infections by entrapping in them the macrophage modulators, and as carriers of antibiotics in treatment of intracellular infections that reside in MPS. This must further be enhanced by grafting on the liposome surface the ligands, e.g. tuftsin, that not only binds specifically to the MPS cells but also enhances their natural killer activity. Keeping this in view, we designed and developed tuftsin-bearing liposomes as drug carriers for the treatment of macrophage-based infections and outline these studies in this overview.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Tuftsin-bearing liposomes as rifampin vehicles in treatment of tuberculosis in mice

The antitubercular activity of rifampin was considerably increased when it was encapsulated in egg phosphatidylcholine liposomes. A further increase in the activity was observed when the macrophage activator tetrapeptide tuftsin was grafted on the surface of the drug-loaded liposomes. Intermittent treatments (twice weekly) with these preparations were significantly more effective than the continuous treatments. Rifampin delivered twice weekly for 2 weeks in tuftsin-bearing liposomes was at least 2,000 times more effective than the free drug in lowering the load of lung bacilli in infected animals. However, pretreatment with drug-free tuftsin-bearing liposomes did not render the pretreated animals resistant to the Mycobacterium tuberculosis infections, neither did it appreciably increase the chemotherapeutic efficacy of the liposomized rifampin. These results clearly demonstrate that liposome targeting to macrophages could considerably increase the antitubercular activity of liposomized drugs such as rifampin. Also, it shows that immunoprophylactic treatment with macrophage activators such as tuftsin does not afford any advantage in treatment of tuberculosis infections, presumably because of inactivation of the primed macrophages by the mycobacterial sulfatides.

Tuftsin-bearing liposomes as drug vehicles in the treatment of experimental aspergillosis

Encapsulation of amphotericin B in tuftsin-bearing liposomes greatly increased its efficacy in treatment of human aspergillosis in mice. Also, the drug efficacy was significantly increased by pretreating the animals with drug-free tuftsin-bearing liposomes. These results demonstrate that macrophage activation can considerably enhance the therapeutic efficacy of antifungal drugs, like amphotericin B.