Biomedical subjects

J K Hendricks

Publications and source records attributed to J K Hendricks.

5 recordsLinked to original sources

PubMed2002

Biocompatible semiconductor optoelectronics.

We investigate optoelectronic properties of integrated structures comprising semiconductor light-emitting materials for optical probes of microscopic biological systems. Compound semiconductors are nearly ideal light emitters for probing cells and other microorganisms because of their spectral match to the transparency wavelengths of biomolecules. Unfortunately, the chemical composition of these materials is incompatible with the biochemistry of cells and related biofluids. To overcome these limitations, we investigate functionalized semiconductor surfaces and structures to simultaneously enhance light emission and the flow of biological fluids in semiconductor microcavities. We have identified several important materials problems associated with the semiconductor/biosystem interface. One is the biofluid degradation of electroluminescence by ionic diffusion into compound semiconductors. Ions that diffuse into the active region of a semiconductor light emitter can create point defects that degrade the quantum efficiency of the radiative recombination process. In this paper we discuss ways of mitigating these problems using materials design and surface chemistry, and suggest future applications for these materials.

Animals↗

PubMed2001

Human mesenchymal stem cells maintain transgene expression during expansion and differentiation.

Human adult bone marrow contains both hematopoietic stem cells that generate cells of all hematopoietic lineages and human mesenchymal stem cells (hMSCs), which support hematopoiesis and contribute to the regeneration of multiple connective tissues. The goal of the current study was to demonstrate that transduced hMSCs maintain transgene expression after stem cell differentiation in vitro and in vivo. We have introduced genes into cultured hMSCs by retroviral vector transfer and demonstrated long-term in vitro and in vivo expression of human interleukin 3 (hIL-3) and green fluorescent protein (GFP). Protocols were developed to achieve transduction efficiencies of 80-90% in these stem cells. In vitro expression of hIL-3 averaged 350 ng/10(6)cells/24 h over 17 passages (> 6 months) and GFP expression was stable over the same time period. Transduced hMSCs were able to differentiate into osteogenic, adipogenic, and chondrogenic lineages and maintained transgene expression after differentiation. Parallel studies were performed in vivo using NOD/SCID mice. Human MSCs expressing hIL-3 were cultured on several matrices and then delivered by subcutaneous, intravenous, and intraperitoneal routes. Sampling of peripheral blood demonstrated that systemic hIL-3 expression was maintained in the range of 100-800 pg/ml over a period of 3 months. These results illustrate the ability of hMSCs to express genes of therapeutic potential and demonstrate their potential clinical utility as cellular vehicles for systemic gene delivery.

Adult↗

PubMed2000

Mesenchymal stem cells as vehicles for gene delivery.

Mesenchymal stem cells contribute to the regeneration of mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon, adipose, and marrow stroma. Transduction of mesenchymal stem cells from species other than humans is required for the development of disease models in which mesenchymal stem cells-based gene delivery is evaluated. Attempts to transduce mesenchymal stem cells from some species with amphotropic retroviral vectors were unsuccessful, leading to comparative mesenchymal stem cells transductions with xenotropic and gibbon-ape leukemia virus envelope-pseudotyped retroviral vectors. Human, baboon, canine, and rat mesenchymal stem cells were transduced optimally with amphotropic vector supernatants. In contrast, sheep, goat, and pig mesenchymal stem cells showed highest transduction levels with xenotropic retroviral vector supernatant, and rabbit mesenchymal stem cells were transduced optimally with gibbon-ape-enveloped vectors. Using a myeloablative canine transplantation model and gene-marked canine mesenchymal stem cells, the biodistribution of infused and ex vivo expanded mesenchymal stem cells were examined. The majority of transduced canine mesenchymal stem cells were found in the bone marrow samples. The current study shows the use of mesenchymal stem cells as a delivery vehicle for gene transfer studies, and validates the feasibility of delivering mesenchymal stem cells to the marrow compartment for stromal regeneration after cancer-associated cytotoxic therapies.

Animals↗

PubMed1997

Helicobacter pylori ABC transporter: effect of allelic exchange mutagenesis on urease activity.

Helicobacter pylori urease requires nickel ions in the enzyme active site for catalytic activity. Nickel ions must, therefore, be actively acquired by the bacterium. NixA (high-affinity nickel transport protein)-deficient mutants of H. pylori retain significant urease activity, suggesting the presence of alternate nickel transporters. Analysis of the nucleotide sequence of the H. pylori genome revealed a homolog of NikD, a component of an ATP-dependent nickel transport system in Escherichia coli. Based on this sequence, a 378-bp DNA fragment was PCR amplified from H. pylori genomic DNA and used as a probe to identify an H. pylori lambda ZAPII genomic library clone that carried these sequences. Four open reading frames of 621, 273, 984, and 642 bp (abcABCD) were revealed by sequencing and predicted polypeptides of 22.7, 9.9, 36.6, and 22.8 kDa, respectively. The 36.6-kDa polypeptide (AbcC) has significant homology (56% amino acid sequence identity) to an E. coli ATP-binding protein component of an ABC transport system, while none of the other putative proteins are significantly homologous to polypeptides in the available databases. To determine the possible contribution of these genes to urease activity, abcC and abcD were each insertionally inactivated with a kanamycin resistance (aphA) cassette and allelic exchange mutants of each gene were constructed in H. pylori UMAB41. Mutation of abcD resulted in an 88% decrease in urease activity to 27 +/- 31 mumol of NH3/min/mg of protein (P < 0.0001), and a double mutant of nixA and abcC resulted in the near abolishment of urease activity (1.1 +/- 1.4 mumol of NH3/min/mg of protein in the double mutant versus 228 +/- 92 mumol of NH3/min/mg of protein in the parent [P < 0.0001]). Synthesis of urease apoenzyme, however, was unaffected by mutations in any of the abc genes. We conclude that the abc gene cluster, in addition to nixA, is involved in production of a catalytically active urease.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

The precursor protein of the structural apolipoproteins of lipophorin: cDNA and deduced amino acid sequence.

A 10 138 bp cDNA from the fat body of the tobacco hornworm, Manduca sexta, which encodes the precursor protein for apolipophorin aPOLP-1 and -II, the structural apolipoproteins of the insect lipoprotein, lipophorin, has been cloned and sequenced. The cDNA has a single 9915 bp open reading frame beginning at an initiating ATG at bp 59 and extending to a stop codon at position 9974. This open reading frame encodes a 3305 amino acid protein with a molecular mass of 366 812 Da. Signal peptide cleavage is predicted to occur after residue 23, leaving a 3,282 amino acid precursor protein. The precursor protein is arranged with apoLp-II at the amino terminal end and apoLp-I at the carboxy terminal end. At present, the site of cleavage of the precursor protein to generate apoLp-I and -II is unknown.

Amino Acid Sequence↗