Pharmacokinetics and tissue distribution of zidovudine in rats following intravenous administration of zidovudine myristate loaded liposomes

Liposomes accumulating in the reticuloendothelial system (RES) appear to be a promising vehicle to improve the therapeutic index of anti-HIV drugs such as zidovudine (AZT). Since the entrapment efficiency of AZT in liposomes was found to be low and AZT leakage from liposomes is fast, zidovudine myristate (AZT-M) was synthesized as a prodrug, and AZT-M incorporated liposomes in a lyophilized form were prepared with an average diameter of 90 nm and an encapsulation efficiency of 98% after reconstitution. The pharmacokinetic profiles and tissue distribution of AZT after i.v. administration of AZT-M liposomes in rats were investigated, and the results were compared with those after i.v. administration of AZT solution. AZT levels in plasma were significantly higher following application of AZT-M liposomes compared with AZT solution, and AUC0_infinity increased from 5.0 +/- 0.7 micromol x min x ml(-1) to 8.2 +/- 1.7 micromol x min x ml(-1) accordingly. Tissue distribution studies also confirmed higher concentrations of AZT in organs of RES and brain, suggesting that AZT-M liposomes might be promising candidates for therapy of HIV infections.

[Comparison between colorimetry and HPLC on the stability test of roxithromycin]

AIM

To compare the stability of roxithromycin in solutions of different pH.

METHODS

Roxithromycin solutions of different pH were prepared with water, simulate intestinal fluid (SIF) and simulate gastric fluid (SGF) shown to be the stability of these solutions were tested by colorimetry and HPLC.

RESULTS

Roxithromycin was stable in water, SGF and SIF determined by colorimetry. However, it was found to be stable only in water and SIF but unstable in SGF as determined by HPLC.

CONCLUSION

Roxithromycin is unstable in acidic medium like SGF. The metabolite of roxithromycin showed unfavorable interference on the assay of roxithromycin when colorimetry was used. Colorimetry can not be used for the determination and assay of roxithromycin in acidic solution like SGF.

[Studies on melatonin gelatin microspheres for intranasal administration]

AIM

To increase the bioavailability of melatonin (MT), MT gelatin microspheres (MT-GMS) for intranasal administration were prepared.

METHODS

MT-GMS were prepared using emulsifying-cross linking technique. Orthogonal tests were used to optimize the preparation conditions. The residence time of technetium-99m (99mTc) labeled gelatin microspheres (GMS) in the nasal cavity of rabbits as compared to gelatin solution, was investigated using gamma scintigraphy. Furthermore the bioavailability in rabbits was examined for evaluating MT-GMS.

RESULTS

The mean diameter of MT-GMS was 50.2 microns, the particle size focused on 30-70 microns. The drug content was 13.48%. The release profile in vitro showed sustained effect. The residence time of GMS in the nasal cavity of rabbits was longer than that of gelatin solution. After intranasal administration in rabbits, the bioavailability of MT-GMS was 87.47% as compared to vein injection, while the bioavailability of MT solution was 69.72%.

CONCLUSION

MT-GMS prepared could meet the needs of intranasal administration, and could increase the bioavailability of MT.

Sequence analysis of a fragment of rOmpA gene of several isolates of spotted fever group rickettsiae from China

The nucleotide sequence of rOmpA gene fragment of three Chinese isolates of spotted fever group rickettsiae (SFGR) (BJ-90, Ha-91 and HLJ-054) was determined. The obtained nucleotide and putative amino acid sequences were compared with those of another Chinese SFGR isolate (HL-93) and several prototype SFGR strains. This comparison showed that the isolates BJ-90 and Ha-91 are closely related to each other and R. sibirica but different from the isolates HLJ-054 and HL-93. We assume that with exception of the isolates HLJ-054 and HL-93 that represent new, unique members of SFGR, the isolates BJ-90 and Ha-91 are closely related to R. sibirica, one of the prototype SFGR strains.

Detection of Rickettsia sibirica in ticks and small mammals collected in three different regions of China

The primers Rr 190.70p and Rr 190.602n were used to detect spotted fever group (SFG) rickettsiae by polymerase chain reaction (PCR) in ticks and small mammals collected in three different regions of China. The obtained results indicated that specific DNA fragments of SFG rickettsiae were amplified from Dermacentor silvarum, D. sinicus, D. auratus, Haemaphysalis concinna, H. wellingtoni, H. yeni, Apodemus agrarius, Microtus fortis. Clethrionomys rufocanus, Ondatra zibethica, Rattus flavipectus and hedgehog. The PCR product were digested with restriction endonucleases PstI and RsaI and the obtained electrophoretic profiles were compared with those of the prototype strains of SFG rickettsiae by the restriction fragment length polymorphism (RFLP) technique. The comparisons showed that the profiles were identical to those of Rickettsia sibirica. In addition, three new isolates of R. sibirica were obtained from H. yeni, D. sinicus and hedgehog, and designated NH-95, BJ-95 and BHJ-95, respectively. These results not only demonstrated a horizontal transmission of the rickettsiae between ticks and hosts but also suggested that R. sibirica is widely distributed in China and its hosts and vectors are various, all that indicating the existence of natural foci of North Asia tick-borne spotted fever specific to China.

[A molecular epidemiologic investigation of north Asia fever in scenic spots of Beijing suburb]

PCR/RFLP technique was used to detect spotted fever group rickettsiae (SFGR) in ticks and small mammals collected in eleven scenic spots of Beijing suburb. We not only detected Rickettsia sibirica in D. sinicus and hedgehog collected nearby the Museum of Aviation, but also isolated two strains of SFGR from them, named as BJ-95 strain and BJH-95 strain respectively. The two strains were identified as R. sibirica by SDS-PAGE, Western blot and PCR/RFLP. The results demonstrated the existence of horizontal transmission of R. sibirica between ticks and small mammals and showed the most scenic spots except the vicinity of Museum of Aviation being investigated were safe to North Asia Fever. This is the first report on the isolation of R. sibirica in hedgehogs.

Sequence analysis and comparison of 190 K surface antigen gene fragment of a new species of spotted fever group rickettsiae

A 533 bp long PCR product amplified from rickettsial strain HL-93 DNA with the primer pair Rr 190.70p and Rr 190.602n, designed from DNA sequence encoding 190 K protein antigen of R. rickettsii, was cloned into plasmid vector PGEM-T and sequenced. The primer-flanking region of the product, an open reading frame, was 491 bp long. The sequence of the product was compared with those of the corresponding regions of DNAs of R. rickettsii (strain R), R. japonica (strain VR 1363) and R. conorii (strain Malish 7) which were reported earlier by other authors. The results showed that 23, 31 and 52 nucleotides in the compared sequence in strain HL-93 differed from those in R. japonica, R. rickettsii and R conorii, respectively. The homologies of strain HL-93 with R. japonica, R. rickettsii and R. conorii were 95.6%, 94% and 90% in nucleotide, and 89%, 87% and 80% in putative amino acid sequences. We consider strain HL-93 as a new member of the spotted fever group (SFG) rickettsiae on the basis of a high degree of homology and genetic divergence in the nucleotide sequence of a part of the 190 K protein gene.

Genotypic identification of three new strains of spotted fever group rickettsiae isolated in China

Polymerase chain reaction (PCR) and restriction endonuclease fragment length polymorphism (RFLP) analysis were used to characterize the genotypic diversity of three isolates of spotted fever group (SFG) rickettsiae isolated from ticks in China. A primer pair designed from DNA sequence encoding 190 K protein antigen of R. rickettsii and genomic DNAs obtained from the isolates were used in PCR. The PCR products were cleaved with restriction endonucleases PstI and RsaI, and the digestion patterns were analyzed by polyacrylamide gel electrophoresis (PAGE) and compared with those of all known species and strains of SFG rickettsiae. The results showed that three isolates had the same PCR products as the other SFG rickettsiae under comparison. HL-93 strain, isolated from Hemophysalis concinna ticks collected in Hulin County, Heilongjiang Province, had unique PstI digestion pattern among SFG rickettsiae; strains BJ-93 and 053, isolated from Dermacentor sinicus and Haemaphysalis concinna ticks collected in Changping County, Beijing City, and Suifenhe City, Heilongjiang Province, respectively, had the same PstI and RsaI digestion patterns as strains R. sibirica 246, BJ-90 and IMTO-85. The present study demonstrated that the BJ-93 and 053 strains were genotypically identical with R. sibirica and the HL-93 strain was genotypically unique among SFG rickettsiae.

Detection of spotted fever group rickettsiae in ticks and rodents by polymerase chain reaction technique in People's Republic of China

The polymerase chain reaction (PCR) technique for amplification of genomic fragments of spotted fever group (SFG) rickettsiae directly from field samples of ticks, tick ova, tick larvae, tick faeces and organs of wild mice was employed for the first time in P.R. of China. Ticks and rodents were collected in Beijing and Heilongjiang, Hainan and Hebei Provinces. The PCR primers were designed from the DNA sequence encoding the 190 K protein of R. rickettsii for a 532 bp long product. Seven of ten tick samples, three of four tick ovum samples, one of two tick larva samples, four of seven tick faeces samples (the samples represented pools of several individuals), and two of twenty-seven wild mouse organs were found PCR-positive. In comparison with PCR assay, the haemolymph test gave similar but not so clear-cut results. PCR assay is recommended as a rapid, sensitive and convenient tool for the detection of SFG rickettsiae in endemic foci. The fact that tick faeces were found to certain extent PCR-positive for the presence of SFG rickettsiae is apparently the first report on this subject and contributes to the knowledge of the transmission of these micro-organisms in the nature.

[The application of PCR to epidemiological study on spotted fever group rickettsiae]

It was the first time that a primer pairs derived from the 190KDa protein antigen gene of R. rickettsii were used to amplify SFGR DNA in ticks, tick ova, larva, tick faeces and rodent organs which were collected in Hebei, Heilongjiang, Hainan and Beijing. A 532bp fragment was respectively amplified from above samples. The results were partially in concordance with data obtained through rickettsiae isolation. It was suggested that PCR is a rapid, specific, sensitive and practical method for detection of SFGR in endemic foci.

Genotypic identification of seven Rickettsia conorii strains

Restriction endonuclease fragment length polymorphism (RFLP) analysis and polymerase chain reaction (PCR) were used to characterize the genotypic diversity of 7 strains of Rickettsia conorii from South Africa, Ethiopia, Morocco, India and Russia. The strains of R. conorii were divided into four genotypes by Rsa I or Pst I endonuclease digestion of PCR-amplified rickettsial DNA using primers derived from the R. rickettsii 190 K antigen gene. M-1 and Barbash strains were genotypically identical, but different from Indian, Ethiopian and S7 strains, which formed another group. Simko and Moroccan strains were genotypically different from each other and also from other strains of R. conorii. We conclude that there exist a genotypic diversity among intraspecies of R. conorii.

[Isolation and identification of the W-88 strain of spotted fever group rickettsiae from a human case in Tongliao City, Inner Mongolia]

One strain of spotted fever group (SFG) rickettsiae was isolated from a patient with febrile and headache who was missdiagnosed as common cold. The rickettsia was isolated by inoculation of yolk sacs of embryonated hen eggs with the patient's blood. The isolate was named as W-88 following the initial letter of the patient's name. It is the first time to report the isolation of SFG rickettsiae from human being who lived in city in China. In this study we compared the antigens of W-88 strain with seven prototype strains of SFG rickettsiae and six Chinese strains of SFG rickettsiae with one species-specific monoclonal antibody and one group reactive monoclonal antibody by indirect-immunofluorescence assay. The results demonstrated that W-88 strain and other Chinese strains JH-74, An-84, FT-84, MT-84, Se-85, To-85 of SFG rickettsiae were found identical to Rickettsia sibirica (strains 232 and 246) and differ from other prototypes of SFG rickettsiae.