HIV and malaria co-infection: interactions and consequences of chemotherapy.

The global epidemiology of HIV/AIDS and malaria overlap because a significant number of HIV-infected individuals live in regions with different levels of malaria transmission. Although the consequences of co-infection with HIV and malaria parasites are not fully understood, available evidence suggests that the infections act synergistically and together result in worse outcomes. The importance of understanding chemotherapeutic interactions during malaria and HIV co-infection is now being recognized. We know that some antimalarial drugs have weak antiretroviral effects; however, recent studies have also demonstrated that certain antiretroviral agents can inhibit malaria-parasite growth. Here, we discuss recent findings on the impact of HIV/AIDS and malaria co-infection and the possible roles of chemotherapy in improving the treatment of these diseases.

Stronger activity of human immunodeficiency virus type 1 protease inhibitors against clinical isolates of Plasmodium vivax than against those of P. falciparum.

Recent studies using laboratory clones have demonstrated that several antiretroviral protease inhibitors (PIs) inhibit the growth of Plasmodium falciparum at concentrations that may be of clinical significance, especially during human immunodeficiency virus type 1 (HIV-1) and malaria coinfection. Using clinical isolates, we now demonstrate the in vitro effectiveness of two HIV-1 aspartic PIs, saquinavir (SQV) and ritonavir (RTV), against P. vivax (n = 30) and P. falciparum (n = 20) from populations subjected to high levels of mefloquine and artesunate pressure on the Thailand-Myanmar border. The median 50% inhibitory concentration values of P. vivax to RTV and SQV were 2,233 nM (range, 732 to 7,738 nM) and 4,230 nM (range, 1,326 to 8,452 nM), respectively, both within the therapeutic concentration range commonly found for patients treated with these PIs. RTV was fourfold more effective at inhibiting P. vivax than it was at inhibiting P. falciparum, compared to a twofold difference in SQV sensitivity. An increased P. falciparum mdr1 copy number was present in 33% (3/9) of isolates and that of P. vivax mdr1 was present in 9% of isolates (2/22), but neither was associated with PI sensitivity. The inter-Plasmodium sp. variations in PI sensitivity indicate key differences between P. vivax and P. falciparum. PI-containing antiretroviral regimens may demonstrate prophylactic activity against both vivax and falciparum malaria in HIV-infected patients who reside in areas where multidrug-resistant P. vivax or P. falciparum is found.

Potent antimalarial activity of histone deacetylase inhibitor analogues.

The malaria parasite Plasmodium falciparum has at least five putative histone deacetylase (HDAC) enzymes, which have been proposed as new antimalarial drug targets and may play roles in regulating gene transcription, like the better-known and more intensively studied human HDACs (hHDACs). Fourteen new compounds derived from l-cysteine or 2-aminosuberic acid were designed to inhibit P. falciparum HDAC-1 (PfHDAC-1) based on homology modeling with human class I and class II HDAC enzymes. The compounds displayed highly potent antiproliferative activity against drug-resistant (Dd2) or drug sensitive (3D7) strains of P. falciparum in vitro (50% inhibitory concentration of 13 to 334 nM). Unlike known hHDAC inhibitors, some of these new compounds were significantly more toxic to P. falciparum parasites than to mammalian cells. The compounds inhibited P. falciparum growth in erythrocytes at both the early and late stages of the parasite's life cycle and caused altered histone acetylation patterns (hyperacetylation), which is a marker of HDAC inhibition in mammalian cells. These results support PfHDAC enzymes as being promising targets for new antimalarial drugs.

Synergistic interactions of the antiretroviral protease inhibitors saquinavir and ritonavir with chloroquine and mefloquine against Plasmodium falciparum in vitro.

The antimalarial activity of several antiretroviral protease inhibitor combinations was investigated. Data demonstrate that ritonavir and saquinavir behave synergistically with chloroquine and mefloquine. These data, and interactions with pepstatin-A, E-64, and bestatin, suggest that human immunodeficiency virus protease inhibitors do not target digestive-vacuole plasmepsins.

Malaria in the post-genomics era: light at the end of the tunnel or just another train?

Malaria remains the third leading cause of death attributable to an infectious disease worldwide, with an estimated death toll of over 2 million per year, predominately in sub-Saharan Africa. The first serious attempt to eradicate this disease was unsuccessful, and 50 years later in 1998 a second programme coined "roll back malaria" was started. While this programme is at present unlikely to reach its stated aims, the completion of the genome sequencing projects on the human host, the mosquito vector, and the malaria parasite offers new hope. It is probable that the burden of disease caused by the most malignant form of the parasite Plasmodium falciparum can be, if not eliminated, then effectively suppressed within a generation through new and novel treatments aimed at all three arms of malaria control.

Inhibition of Plasmodium falciparum clag9 gene function by antisense RNA.

We have previously shown by targeted gene disruption that the clag9 gene of Plasmodium falciparum is essential for cytoadherence to CD36. Here we report inhibition of the function of clag9 by the use of an antisense RNA vector as an alternative to targeted gene disruption. We transfected an antisense construct of clag9 into the P. falciparum clone 3D7 and when the resulting line was cultured in the presence of pyrimethamine it showed 15-fold lower cytoadherence to C32 melanoma cells than the control. Reversion to wildtype upon removal of the introduced plasmid provides direct evidence that the event responsible for the phenotypic change is not at an unrelated site and this approach provides a valuable new tool in malaria transfection technology.

clag9: A cytoadherence gene in Plasmodium falciparum essential for binding of parasitized erythrocytes to CD36.

The propensity of isolates of the malaria parasite Plasmodium falciparum to delete a segment of chromosome 9 has provided positional information that has allowed us to identify a gene necessary for cytoadherence. It has been termed the cytoadherence-linked asexual gene (clag9). clag9 encodes at least nine exons and is expressed in blood stages. The hydrophobicity profile of the predicted CLAG9 protein identifies up to four transmembrane domains. We show here that targeted gene disruption of clag9 ablated cytoadherence to C32 melanoma cells and purified CD36. DNA-induced antibodies to the clag9 gene product reacted with a polypeptide of 220 kDa in the parental malaria clone but not in clones with a disrupted clag9 gene.

The cytoadherence linked asexual gene family of Plasmodium falciparum: are there roles other than cytoadherence?

The binding of erythrocytes infected with Plasmodium falciparum to the endothelium lining the small blood vessels of the brain and other organs can mediate severe pathology. A region at the right end of chromosome 9 has been implicated in the binding of parasitised erythrocytes to the endothelial receptor CD36. A gene expressed in asexual erythrocytic stage parasites has been identified in this region and termed the cytoadherence linked asexual gene (clag). Antisense RNA production and targeted gene disruption of clag resulted in greatly reduced binding to CD36. Hybridisation to 3D7 chromosomes showed clag to be a part of a gene family of at least nine members. All members analysed so far have a conserved gene structure of at least nine exons, as well as putative transmembrane domains. The possible functions of the gene family are discussed.

Group A streptococcal Vir types are M-protein gene (emm) sequence type specific.

The M-protein genes (emm genes) of 103 separate impetiginous Streptococcus pyogenes isolates were sequenced and the sequence types were compared to the types obtained by Vir typing. Vir typing is based on restriction fragment length polymorphism (RFLP) analysis of a 4- to 7-kb pathogenicity island encoding emm and other virulence genes. By using both HaeIII and HinfI to generate RFLP profiles, complete concordance between Vir type and emm sequence type was found. Comparison of the emm sequences with those in GenBank revealed new sequence types sharing less than 90% identity with known types. Diversity in the emm sequence was generated by corrected frameshift mutations, point mutations, and small in-frame mutations.

Lack of polymorphism within the rRNA operons of group A streptococci.

Polymerase chain reaction (PCR) ribotyping of many bacterial species has shown that polymorphism of the ribosomal RNA (rRNA) operons, within and between strains, is common. Restriction fragment length polymorphism (RFLP) analysis of the rRNA operons of thirty-two genetically and geographically distinct strains of group A streptococci (GAS) revealed that there are only two major HaeIII PCR-ribotypes. This variation is due to a single nucleotide change within the 16S-23S intergenic spacer regions of these operons. As in many other bacterial species, this spacer region in streptococci also contains the gene for tRNA(ala). Within each GAS isolate, hybridization results are consistent with the presence of six rRNA operons. Interestingly, for a given strain, irrespective of its origin, all six rRNA operons have the same RFLP pattern. This contrasts with the findings in many other bacteria species, where heterogeneity of the rRNA operons within a genome is a common feature. This lack of heterogeneity of rRNA operons in an organism that is known to acquire genetic sequences through horizontal transfer is intriguing.

Clinical regeneration with guided tissue barriers.

This review of the current periodontal literature evaluates clinical regeneration with guided tissue barriers in infrabony defects and furcations. A meta-analysis was conducted by calculating weighted means with confidence intervals for each treatment group. Clinical improvement in infrabony defects was best for polylactic acid/polyglactin (PLA/PGA) barriers, with a mean pocket reduction of 5.3 mm and a mean gain in clinical probing attachment level of 4.7 mm. For furcations, special attention was given to the frequency of either complete or partial (> or = 50%) furcation closure. Complete furcation closure was an infrequent result of guided tissue regeneration, occurring in only 7% to 19% of furcations treated with barriers. For the time period reported, the best clinical results in furcations and infrabony defects occurred with PLA/PGA-type barriers. However, there were no statistically significant differences among the various barriers in infrabony defects or furcations.

Current trends in endodontic treatment: report of a national survey.

The authors surveyed 360 general dentists and 291 endodontists to obtain information on routine, nonemergency endodontic treatments adapted to clinical practice. Frequent practices and recent advances in treatment modalities-including instrumentation, obturation, intracanal preparations, medications and restorations-are highlighted.

Molecular epidemiology of impetiginous group A streptococcal infections in aboriginal communities of northern Australia.

Group A streptococcal infections among the Aboriginal communities of the Northern Territory of Australia are endemic, with a concurrently high rate of the postinfection sequelae of rheumatic fever and acute post-streptococcal glomerulonephritis. The majority of the group A streptococcal isolates from the Northern Territory are not typeable by M typing. We recently developed a novel genotyping method, Vir typing. A preliminary study using this method discriminated all the M-nontypeable (MNT) isolates. Vir typing is based on restriction fragment length polymorphisms of the 4- to 7-kb Vir regulon of group A streptococci, which contains a number of genes, including emm (the gene for M protein). A total of 407 isolates of group A streptococci obtained from four Aboriginal communities over a 4-year period were typed by this genotyping method. Forty-two distinct genotypes were found among the isolates, including 22 among the MNT isolates. The correlation between Vir type and M type was good. This genotyping method allows the characterization of all group A streptococcal isolates from Aboriginal communities in the Northern Territory. We also propose that Vir typing be used in conjunction with M typing for epidemiological surveillance in geographical regions where the majority of isolates are MNT.

Frequency of furcation closure with regenerative periodontal therapy.

A review of the literature was performed related to the frequency of closure of Grade II furcations with various regenerative therapies such as bone replacement grafts (BRG), coronally positioned flaps (CPF), guided tissue regeneration barriers (GTR), or open flap debridement (OFD). Fifty papers involving 1,016 furcations were evaluated. Complete furcation closure was reported only 20% of the time. Clinical change from Grade II to Grade I (partial furcation fill) was found in an additional 33% of the cases. Therefore, general improvement in clinical furcation status has been reported only about 50% of the time. The most effective furcation regenerative therapy was the combination of GTR plus BRG (91% overall positive). Similar overall positive results (88%) were achieved with nondemineralized allogeneic freeze-dried bone plus tetracycline without a barrier. The least effective therapy for regeneration in furcations was OFD (2% complete furcation closures and 13% partial furcation closures). If complete furcation closure is a primary goal of regenerative therapy, that goal would not appear to be commonly met.