Biomedical subjects
Publications and source records attributed to K Parikh.
We study the sedimentation of two identical but nonspherical particles sedimenting in a Stokesian fluid. Experiments and numerical simulations reveal periodic orbits wherein the bodies mutually induce an in-phase rotational motion accompanied by periodic modulations of sedimentation speed and separation distance. We term these "tumbling orbits" and find that they appear over a broad range of body shapes.
Previous studies in rodents and non-human primates have demonstrated that pretreatment of animals with cholinesterases could provide significant protection against organophosphate (OP) nerve agent toxicity. Gene delivery/therapy is emerging as an approach to achieve high-level expression of proteins in vivo that are very similar to their native counterparts. Recently, adenoviral (Ad) vectors have proven to be excellent vehicles for delivering genes to cells in vitro and in vivo. In this study, we explored the use of the newly designed AdenoVATOR system for the expression of recombinant human butyrylcholinesterase (rHu BChE) in human embryonic kidney 293A (HEK-293A) cells. In these cells, rHu BChE was expressed as mostly tetrameric form by the simultaneous expression of proline-rich attachment domain. By optimizing the culture conditions, 1.5-2.0 U/ml of rHu BChE could be expressed in HEK-293A cells. Recombinant Hu BChE was purified to homogeneity by ammonium sulfate fractionation followed by affinity column chromatography using procainamide Sepharose and cobalt Sepharose gels. The enzymatic and physico-chemical properties of purified rHu BChE were similar to those of native serum-derived Hu BChE. To determine the suitability of this preparation for use as an antidote against highly toxic nerve agents, its pharmacokinetics were evaluated in mice. Recombinant Hu BChE exhibited a mean residence time of 18.3 h which was 2.5-fold shorter than that observed for native Hu BChE in mice. However, rHu BChE chemically modified with polyethyleneglycol (PEG) displayed a mean residence time of 36.2 h suggesting that PEG-modification can prolong the circulatory stability of rHu BChE. The efficacy of Ad-Hu BChE to induce the production of therapeutic levels of bioscavenger in vivo is under evaluation.
The neuropeptide galanin and its receptors are expressed in the locus coeruleus (LC), a brain area associated with drug dependence and withdrawal. Although galanin peptide mRNA levels do not change during withdrawal, it is not known whether galanin receptor levels are regulated following opiate withdrawal. This study demonstrates that galanin binding in the LC is upregulated by chronic-intermittent morphine administration or by precipitated withdrawal, but not by acute morphine treatment, suggesting that increased activity in the LC may be able to regulate galanin binding sites. Moreover, the increase in galanin binding sites seems to be caused by increased transcription or stabilization of the galanin receptor 1 (GalR1) gene, because there is a dramatic increase in mRNA levels following withdrawal in the LC. It is, therefore, possible that the increase in GalR1 could be an adaptive mechanism that leads to regulation of cAMP levels and possibly firing rate of LC neurons.
Galanin is a neuropeptide with appetitive, antinociceptive and neuroendocrine functions. Galanin and galanin binding sites are present in brain areas that mediate reinforcement, such as nucleus accumbens and ventral tegmental area, as well as locus coeruleus, an area known to be involved in development of drug dependence and withdrawal. This localization, coupled with the observation that there is a strong interaction between morphine and galanin in spinal cord, made it of interest to study whether galanin might have effects on morphine reinforcement. Using the place preference paradigm we found that galanin (1 microg i.c.v.) alone does not possess reinforcing or aversive properties but attenuates the preference conditioned by peripheral administration of morphine (5 mg/kg s.c.). Quantitative receptor autoradiography showed that morphine treatment that could condition a place preference decreased galanin binding in the nucleus accumbens and increased galanin binding in the locus coeruleus. In contrast, acute naltrexone administration increased galanin binding in the nucleus accumbens, suggesting that levels of galanin binding are tonically regulated by opioid receptors in that area. Contrary to what is seen in the spinal cord, these results indicate that galanin and morphine have an antagonistic interaction in the brain that results in attenuation of morphine reinforcement by activation of the galaninergic system.
DNA chip arrays hold considerable promise for diagnostic sequencing of polymerase chain reaction (PCR) products. To date, however, arrays have been relatively expensive, complex to use and difficult to interpret, preventing their adaptation to the clinical lab. A moderate density array method has been developed that enables efficient, easy-to-interpret and robust solid-phase PCR product sequencing. Here, the results of Mycobacterium tuberculosis rifampin resistance mutation detection by primer-extension-based sequence scanning of the rpo B gene of M. tuberculosis are presented. Rifampin resistant clinical isolates were identified in as little as 1 h post PCR amplification with visual results detection.
There is a growing and significant demand for reliable, simple and sensitive methods for repeated scanning of a given gene or gene fragment for detection and characterization of mutations. Solid-phase sequencing by single base primer extension of nested GBATM primers on miniaturized DNA arrays can be used to effectively scan targeted sequences for missense, insertion and deletion mutations. This paper describes the use of N-GBA arrays designed to scan the sequence of a 33 base region of exon 8 of the p53 gene (codons 272-282) encompassing a hot spot for mutations associated with the development of cancer. Synthetic DNA templates containing various missense, insertion and deletion mutations, as well as DNA prepared from pancreatic and biliary tumor cells, were genotyped using the exon 8 arrays.
Mycobacterium avium complex (MAC) strains from AIDS and non-AIDS patients and from the environment were studied for their colony morphology and virulence in beige mice. The majority of the MAC isolates from AIDS patients, in contrast to those from non-AIDS patients and the environment, showed increased virulence. Similarly, the majority of the MAC isolates from AIDS patients formed smooth transparent (ST) colonies, whereas most of the non-AIDS isolates formed smooth opaque (SO) or intermediate (IM) type of colonies. MAC isolates from the same AIDS patient obtained at different times were found to be heterogenic with respect to serotype, RFLP and glycolipid patterns, suggesting that these patients might be infected with more than one strain of MAC.
Beige mice were challenged with 10(6)-10(7) cfu of Mycobacterium avium intracellulare strain 101 and 22 days later treated with streptomycin 150 mg/kg/day alone, clofazimine 20 mg/kg/day alone, streptomycin 150 mg/kg/day plus clofazimine 20 mg/kg/day, or no antimicrobial agent (untreated controls). Both single-drug therapies partially reduced the cfu counts in spleen, liver and lungs compared with the controls however the combination was significantly more effective and completely eliminated the pathogen from the spleen and lungs of some animals after eight weeks treatment.
Cancer that recurs after surgery and radiation therapy remains a major problem. The claimed effectiveness of thermobrachytherapy in patients with this problem prompted the present study. Forty-six lesions (20 head and neck, 18 pelvic, seven chest wall, and one limb sarcoma) in 38 patients were treated with interstitial hyperthermia that sandwiched the use of Ir-192 with the aim of delivering 2,000-6,000 cGy, depending on prior dose and tissue tolerance. Complete regression occurred in 19 (54%) of 35 evaluable cases. More than 58,000 measured temperature points were analyzed to develop a representative quantitative measure, the "modal thermal dose," that represented the temperature reported most often during heating sessions. The pattern was plotted in each case. No significant relation was found between heating patterns and tumor response. Of all the prognostic factors studied, the radiation dose was the most significant, with a complete response rate being 78% when the total radiation dose exceeded 6,000 cGy, compared with 8% when the dose was lower than 5,000 cGy (P less than .005). The tumor volume also was important, with smaller lesions responding much better than larger ones (P = .1).
We have studied the susceptibility of beige (C57Bl/6/bgJ/bgJ) mice to a virulent strain of Mycobacterium avium complex (MAC) (101) by intravenous, intraperitoneal, intranasal, oral, and intrarectal routes. Consistent with our earlier findings, intravenous challenge resulted in high mortality and colony-forming unit (CFU) counts of recoverable organisms from spleens, lungs, livers, and lymph nodes, plus high levels of mortality. Intraperitoneal challenge resulted in high organ CFU counts but no mortality. Of relevance to the sexual practice of certain homosexual patients with AIDS is the intrarectal route of inoculation, which resulted in extensive involvement of the visceral organs with MAC disease. Multiple challenges by intravenous, oral, or rectal routes resulted in higher CFU counts than did single exposures.
The effect of diltiazem on digoxin serum concentration was evaluated in 9 patients who had been treated chronically for heart disease with digoxin, 0.25 mg/day. The indications for digoxin therapy were arrhythmias in 5 patients and mild heart failure in the other 4. Renal digoxin clearance was also evaluated in 8 of these patients. Serum digoxin concentration was measured at control, 7 +/- 2 days after initiation of 120 mg/day of diltiazem and 11 +/- 5 days after increasing the dose of diltiazem to 240 mg/day. Serum digoxin concentration was 0.9 +/- 0.4 ng/ml at control, 0.8 +/- 0.4 ng/ml with 120 mg/day of diltiazem, and 0.8 +/- 0.3 ng/ml during therapy with 240 mg/day. The differences between these values were not significant. Renal digoxin clearance also did not show a significant change after diltiazem therapy (44 +/- 15 ml/min before diltiazem and 46 +/- 13 ml/min with 240 mg/day of diltiazem). This study shows no effect of diltiazem in doses of 120 to 240 mg/day on serum digoxin concentration or renal digoxin clearance in patients who are treated chronically for heart disease with digoxin. In this dose range, diltiazem has advantages over verapamil, which markedly elevates digoxin levels.
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