Biomedical subjects

Amir Khan

Publications and source records attributed to Amir Khan.

7 recordsLinked to original sources

PubMed2005

Nitric oxide and reactive oxygen species production causes progressive damage in rats after cessation of silica inhalation.

Our laboratory has previously reported results from a rat silica inhalation study which determined that, even after silica exposure ended, pulmonary inflammation and damage progressed with subsequent fibrosis development. In the present study, the relationship between silica exposure, nitric oxide (NO) and reactive oxygen species (ROS) production, and the resultant pulmonary damage is investigated in this model. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were sacrificed at 0 days postexposure, while another portion was maintained without further exposure for 36 days to examine recovery or progression. The major findings of this study are: (1) silica-exposed rat lungs were in a state of oxidative stress, the severity of which increased during the postexposure period, (2) silica-exposed rats had significant increase in lung NO production which increased in magnitude during the postexposure period, and (3) the presence of silica particle(s) in an alveolar macrophage (AM) was highly associated with inducible nitric oxide synthase (iNOS) protein. These data indicate that, even after silica exposure has ended, and despite declining silica lung burden, silica-induced pulmonary NO and ROS production increases, thus producing a more severe oxidative stress. A quantitative association between silica and expression of iNOS protein in AMs was also determined, which adds to our previous observation that iNOS and NO-mediated damage are associated anatomically with silica-induced pathological lesions. Future studies will be needed to determine whether the progressive oxidative stress, and iNOS activation and NO production, is a direct result of silica lung burden or a consequence of silica-induced biochemical mediators.

Administration, Inhalation↗

PubMed2005

Successful parallel development and integration of a plasmid-based biologic, container/closure system and electrokinetic delivery device.

We have developed three major technologies that allow plasmid-based products to be used for large-scale vaccination or therapeutic protein applications. Our team has integrated these components into one complete, cost-effective, easy-to-use system capable of rapid implementation under field conditions. The proprietary manufacturing process uses a lysis method and membrane-based chromatography to rapidly produce large-scale batches of plasmid. Plasmid doses are filled into the Becton-Dickinson Uniject container/closure system. The Uniject adapts to the electrode array of our constant current electrokinetic device, such that the plasmid is delivered in the area of tissue defined by the electrodes. Thus, plasmid uptake and expression levels are dramatically improved. This is the first completely integrated delivery system for plasmid-based products.

Chromatography, Liquid↗

PubMed2004

Progression of lung inflammation and damage in rats after cessation of silica inhalation.

Human epidemiologic studies have found that silicosis may develop or progress even after occupational exposure has ended, suggesting that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure. We previously described the time course of rat pulmonary responses to silica inhalation as biphasic, the initial phase characterized by increased but controlled pulmonary inflammation and damage. However, after a threshold lung burden was exceeded, rapid progression of silica-induced pulmonary disease occurred. To test the hypothesis that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure we initiated a study to investigate the relationship between silica exposure, the initiation and progression of silica-induced pulmonary disease, and recovery. Rats were exposed to silica (15 mg/m(3), 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were maintained without further exposure for 36 days to examine recovery. The major findings of this study are: (1) silica-exposed rats were not in pulmonary overload, and lung silica burden decreased with recovery; (2) pulmonary inflammation, damage and lipidosis increased with recovery for rats exposed to silica for 40 and 60 days, but not 20 days; (3) histopathology revealed changes in silica-induced alveolitis, epithelial hypertrophy and hyperplasia, and alveolar lipoproteinosis consistent with bronchoalveolar lavage (BAL) endpoints; and (4) pulmonary fibrosis developed even when exposure was stopped prior to its initial development.

Animals↗

PubMed2002

A characterization of the lumenal region of human tapasin reveals the presence of two structural domains.

Tapasin is a type I membrane glycoprotein involved with other accessory proteins in the assembly of class I MHC-beta(2)m-peptide complexes in the endoplasmic reticulum. We have probed the three-dimensional structure of the lumenal region of human tapasin (residues 1-392) tagged with a (His)(6) sequence at its C-terminus using biochemical and biophysical techniques. The far-UV circular dichroism spectrum revealed that tapasin possesses well-defined secondary structural elements corresponding predominantly to beta-sheets. A thermal denaturation curve recorded at 216 nm showed a midpoint transition centered at approximately 45 degrees C. Sedimentation analysis showed that tapasin is monomeric in solution with a sedimentation coefficient, S degrees (20,w), of 2.68 S. This value of S degrees (20,w) combined with the value of the molar mass obtained by MALDI mass spectrometry (44.2 kDa) yielded a frictional ratio, f/f(0), of 1.47. Assuming tapasin is a prolate ellipsoid, we calculated an apparent length of 22.5 nm and a diameter of 2.62 nm, consistent with an elongated molecular shape. Controlled proteolysis using various enzymes revealed that a narrow region of tapasin near residue 90 is highly susceptible to digestion, resulting in two fragments that are resistant to further cleavage. The identity of these fragments was determined by amino acid sequencing and MALDI mass spectrometry and revealed a 9 kDa N-terminal fragment and a 34 kDa C-terminal fragment. Collectively, these results suggest that tapasin is comprised of two core domains of different sizes loosely linked by a flexible region.

Antiporters↗

PubMed2002

Susceptibility to the ototoxic properties of toluene is species specific.

Toluene is the most widely used industrial solvent. It has been shown to be ototoxic in mice and rats, and to increase permanent threshold shift in conjunction with exposure to noise. Chinchillas are widely used for studying noise effects on the cochlea. The present study was initiated to study toluene and noise interaction in chinchillas. Thirty-three chinchillas were exposed to a 95 dBA 500 Hz octave band noise plus 2000 ppm toluene, 8 or 12 h per day for 10 days. Auditory function was estimated using the auditory brainstem response (ABR) to tones between 500 Hz and 16 kHz. There was no effect on the ABR of toluene alone. Noise alone produced a threshold shift. There was no interaction of noise and toluene on the ear. The present study suggests that chinchillas are markedly less susceptible to the ototoxic effect of toluene than mice and rats. A working hypothesis as to the species differences was that chinchilla liver was able to detoxify the toluene. Hepatic microsomes from chinchillas, rats and humans were tested for their ability to convert toluene to the more water-soluble compound - benzyl alcohol. Chinchilla livers were found to contain more of the P450 enzymes CYP2E1 and CYP2B than rats or humans. In addition, the data show that the P450 enzymes are more active in chinchillas than in rats and humans. In conclusion, the results suggest that rats and mice are a more appropriate model for human toluene ototoxicity. However, chinchillas may provide a valuable model for investigating how ototoxic agents can be detoxified to less damaging compounds.

Animals↗

PubMed2002

Time course of pulmonary response of rats to inhalation of crystalline silica: NF-kappa B activation, inflammation, cytokine production, and damage.

In vitro studies suggest that silica-induced lung disease may be linked to processes regulated by nuclear factor-kappa B (NF-kappa B) activation, but this has not been examined in vivo. Rats were exposed to a silica aerosol of 15 mg/m(3) (6 h/day, 5 days/wk) for 116 days, and bronchoalveolar lavage (BAL) was conducted at various times during the exposure. Silica-induced pulmonary inflammation and damage were determined by measuring BAL cell differentials and first BAL fluid lactate dehydrogenase (LDH) activity and serum albumin concentrations, respectively. NF-kappa B activation and production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) by BAL cells were also measured. The results demonstrate that NF-kappa B activation occurred after 5 days exposure, and continued to increase thereafter. BAL cell production of IL-1 and TNF-alpha had increased incrementally by 10 and 30 days of exposure, respectively. This elevation continued through 79 days of exposure before further increasing at 116 days of exposure. Pulmonary inflammation and damage in silica-exposed rats were also significantly elevated at 5 days of exposure, further increased at a slow rate through 41 days of exposure, and dramatically increased thereafter. Taken together, the results indicate that the initial molecular response of NF-kappa B activation in BAL cells occurs in response to low levels of silica deposition in the lung and increases more rapidly versus exposure duration than silica-induced pulmonary inflammation, cellular damage, and cytokine production by BAL cells. This suggests that NF-kappa B activation in BAL cells may play an important role in the initiation and progression of silica-induced pulmonary inflammation, cellular damage, and fibrosis.

Animals↗

PubMed2002

Enhanced nitric oxide and reactive oxygen species production and damage after inhalation of silica.

In previous reports from this study, measurements of pulmonary inflammation, bronchoalveolar lavage cell cytokine production and nuclear factor-kappa B activation, cytotoxic damage, and fibrosis were detailed. In this study, we investigated the temporal relationship between silica inhalation, nitric oxide (NO), and reactive oxygen species (ROS) production, and damage mediated by these radicals in the rat. Rats were exposed to a silica aerosol (15 mg/m(3) silica, 6 h/day, 5 days/wk) for 116 days. We report time-dependent changes in 1) activation of alveolar macrophages and concomitant production of NO and ROS, 2) immunohistochemical localization of inducible NO synthase and the NO-induced damage product nitrotyrosine, 3) bronchoalveolar lavage fluid NO(x) and superoxide dismutase concentrations, and 4) lung lipid peroxidation levels. The major observations made in this study are as follows: 1) NO and ROS production and resultant damage increased during silica exposure, and 2) the sites of inducible NO synthase activation and NO-mediated damage are associated anatomically with pathological lesions in the lungs.

Administration, Inhalation↗