Immunolocalization of collagen types I and III in the arterial wall of the rat

Summary Collagen types I and III were located by immunofluorescence procedures in the aorta and coronary arteries of the rat. Type I collagen was most prevalent in the adventitia of the aorta with only small amounts present in the intima and media. Type III collagen appeared to be a significant component in the media of the aorta and also in the adventitia of both blood vessels. The intima and media of the coronary arteries did not stain strongly for either type I or III collagen. Neither staining procedure was altered with preincubation of the sections with hyaluronidase or chondroitinase ABC. These studies indicate that type III collagen is a major component of the adventitia which has previously not been recognized by immunohistochemical techniques, possibly due to masking of collagen staining with glycosaminoglycans.     

Measurement of alpha-keto acids in plasma using an amino acid analyzer

A method for measuring keto acid concentrations in physiological fluids using an amino acid analyzer was developed. After preliminary deproteinization and removal of amino acids, reduction with sodium cyanoborohydride at 105 degrees C resulted in efficient conversion of the keto acids to their corresponding amino acids. In applying the technique to plasma samples, the use of MeOH for deproteinization was necessary to avoid the large losses of keto acids that occurred during precipitation of proteins with perchloric acid. The method was used to follow plasma ketoisocaproate concentrations in rat plasma after administration of leucine, and was sufficiently sensitive to detect concomitant changes in other branched-chain keto acid concentrations.     

Mechanism-Based Inhibition of Ribonucleotide Reductases: New Mechanistic Considerations and Promising Biological Applications

Abstract

Ribonucleotide reductases (RNRs) perform the de novo biosynthesis of 2′-deoxynucleoside 5′-(di or tri)phosphates. Inhibition of RNRs removes a crucial source of genetic components and enhances the probability of salvage incorporation of analogues into DNA. Several laboratories have clarified aspects of the reaction cascades initiated by generation of substrate nucleotide C3′ free radicals by RNRs. New considerations for radical-mediated mechanism-based inhibition and biological applications are discussed.     

Radiosensitization of human T-cell leukemia by thymidine and 41.8 degrees C hyperthermia in vitro

This study tested whether thymidine, a naturally occurring nucleoside metabolite, could increase the sensitivity of human T-cell neoplasms to ionizing irradiation and whether adding 41.8 degrees C hyperthermia (X 1 h) to the combination of thymidine and irradiation would further enhance killing of cells by radiation. The magnitude of cytotoxicity induced directly by thymidine was also evaluated. Finally, the ability of 2'-deoxycytidine to prevent thymidine-induced cytotoxicity and radiosensitization was studied. Using JM and MOLT3, two human T-cell acute lymphoblastic leukemias, it was found that thymidine itself was cytotoxic and the toxicity appeared rapidly upon exposure to the drug (i.e., at 4 h). Thymidine caused significant radiosensitization, and thymidine plus 1 h of 41.8 degrees C hyperthermia enhanced radiation-induced killing significantly more than did thymidine or hyperthermia separately. The addition of 2'-deoxycytidine only partly reversed thymidine-induced killing and did not prevent thymidine-induced radiosensitization. The applicability of these results to the clinical management of T- and null-cell malignancies is discussed, as is the presumed mechanistic basis for these observations relative to deoxyribonucleoside metabolism, NAD metabolism, and inhibition of poly(ADP-ribose) polymerase.     

T-cell responses at the host: tumour interface

The evidence considered here reinforces the conclusion that T-cell responses to tumours involve complex cellular interactions. An attempt to summarize some of these interactions is shown. This emphasizes that not only are the interactions between the effector cell populations complicated, but that the target cell surface is also subject to variation and modification as a result of the immune response. A feature that also emerges from these studies is that most cells apparently responding to or infiltrating a tumour do not necessarily participate in its destruction, and it is in this area that experimental tumour systems have particular value. This also perhaps explains the preoccupation of experimentalists with the identification of 'the' effector cell crucial to tumour rejection. However, there is heterogeneity between systems in terms of the type of rejection response induced, but a logical basis for this heterogeneity is not established. If experimental studies could define the nature of the immune response generated by a tumour in the context of the biological features of the tumour itself, this could lead to the prediction of the immunogenicity and potential for induction of a rejection response for that tumor. Clearly, experimental tumour systems do not provide an exact reflection of the situation with human tumours. However, they may provide systems that illuminate particular aspects of the human response, and give precedents to guide the interpretation of data derived from human systems. This form of assessment is still at an early stage, but developments in the experimental field should provide a framework for the development and exploitation of T-cell responses to tumours.     

A unique element resembling a processed pseudogene

We describe a unique DNA element with structural features of a processed pseudogene but with important differences. It is located within an 8.4-kilobase pair region of chicken DNA containing five histone genes, but it is not related to these genes. The presence of terminal repeats, an open reading frame (and stop codon), polyadenylation/processing signal, and a poly(A) rich region about 20 bases 3' to this, together with a lack of 5' promoter motifs all suggest a processed pseudogene. However, no parent gene can be detected in the genome by Southern blotting experiments and, in addition, codon boundary values and mid-base correlations are not consistent with a protein coding region of a eukaryotic gene. The element was detected in DNA from different chickens and in peafowl, but not in quail, pheasant, or turkey.