A Preliminary Study of Tricyclic Antidepressant (TCA) Ovine FAB for TCA Toxicity

BACKGROUND

Animal studies suggest that tricyclic antidepressant antibody fragments (TCA Fab) may be a useful therapy for tricyclic antidepressant poisoning. The objective of this study is to determine if TCA Fab increases total serum TCA levels without raising free serum TCA levels in human overdose patients, indicating that TCA Fab effectively binds TCA.

METHODS

This was a prospective, dose escalation study of patients with mild to moderate TCA poisoning. Patients were treated with an escalating intravenous infusion totaling 7 or 14 gm of TCA Fab. The outcomes of interest were serum TCA levels (total and free), worsening of TCA toxicity, and adverse effects.

RESULTS

Seven patients were treated with Fab. Infusion of TCA Fab was associated with a dramatic increase in total serum TCA levels, while free TCA levels fell in both dosing groups. There were no significant changes in QRS duration, heart rate or mean arterial pressure associated with the Fab Infusion. Worsening of TCA toxicity did not occur despite marked elevation of total serum TCA concentrations. The two patients with the greatest prolongation of QRS showed a prompt shortening in their QRS duration temporally associated with the Fab infusion. Mild wheezing was observed in one asthmatic patient.

CONCLUSIONS

1) TCA Fab raises total serum TCA levels while lowering free levels in TCA poisoned patients; 2) no toxic effects were associated with the increase in TCA levels and no severe adverse effects were observed during the hospital course following Fab infusion.

A randomized multicenter trial of crotalinae polyvalent immune Fab (ovine) antivenom for the treatment for crotaline snakebite in the United States

BACKGROUND

Current therapy for crotaline snakebite includes antivenin (Crotalidae) polyvalent, an antivenom with numerous adverse effects. We compared the efficacy and safety of 2 dosing regimens with a new antivenom, Crotalinae polyvalent immune Fab (Fab AV).

METHODS

A single dose of Fab AV alone (as-needed [PRN] group) was compared with an initial dose plus repeated treatments during 18 hours (scheduled group) in a multicenter randomized trial. The study included patients with minimal or moderate envenomation by a crotaline snake within the preceding 6 hours, aged 10 years or older, in whom worsening of the envenomation syndrome was observed before Fab AV treatment. After treatment with Fab AV to achieve initial control, patients were randomized to the scheduled or PRN treatment group. Scheduled group patients received additional doses of Fab AV every 6 hours for 3 doses. The PRN group received no planned additional doses of antivenom.

RESULTS

The mean severity score of the 31 patients decreased from 4.35 to 2.39 points (P<.001); there was no difference between scheduled and PRN groups. No patient in the scheduled group received unplanned Fab AV doses, but 8 of 16 patients in the PRN group received unplanned doses (P =.002). Acute reactions occurred in 6 patients (19%), and serum sickness occurred in 6 (23%) of 26 patients who returned for follow-up.

CONCLUSIONS

In the first randomized trial of antivenom in the United States, Fab AV effectively terminated venom effects. Since the unplanned use of Fab AV in the PRN group was common, the treatment regimen may require more than 1 initial dose.

Multicentric reticulohistiocytosis with neurofibroma-like nodules

We describe a patient with multicentric reticulohistiocytosis (MR), who presented with 2 different clinical types of lesions. Some were characteristic for MR in that they were deeply set, small, firm papules. Many others were larger, soft, and even sessile, like neurofibromas. Histopathologic features of both types of lesions revealed MR. To our knowledge, this is the first report of lesions of MR mimicking neurofibromas.

Comparison of the pharmacokinetics and in vivo bioaffinity of DigiTAb versus Digibind

The in vivo digoxin binding affinity and normal pharmacokinetic values of digoxin-immune Fab are unknown. Healthy subjects (n = 16) were randomized to one of the two digoxin-immune Fab products, DigiTAb or Digibind, to compare the in vivo digoxin binding affinity and pharmacokinetic disposition. Each subject received 1 mg of intravenous digoxin infused during 5 minutes followed 2 hours later by 76 mg of either DigiTAb or Digibind. Both Fab products reduced free digoxin serum concentrations to below assay detection with equal ability. Consequently, total digoxin serum concentrations increased approximately 10-fold. Peak total digoxin serum concentrations post-Fab dosing were similar to the pre-Fab peak digoxin concentration for both Fab products (45 +/- 14 and 44 +/- 11 for DigiTAb, pre and post, respectively) 50 +/- 17 and 41 +/- 9 for Digibind, pre and post, respectively) indicating in vivo equimolar binding affinity. While bioaffinity for digoxin was equal between groups, total digoxin area under the curve (AUC) and digoxin-immune Fab AUC were lower in the DigiTAb group compared with the Digibind group. Hence, systemic total digoxin and Fab clearance were greater in the DigiTAb-treated group. In conclusion, equimolar doses of both DigiTAb and Digibind completely bind digoxin in vivo. The ability of digoxinimmune Fab to bind to digoxin is not affected by the systemic disposition of the Fab product.

Chromatin remodeling of the interleukin-2 gene: distinct alterations in the proximal versus distal enhancer regions

Known transcription factor-DNA interactions in the minimal enhancer of the murine interleukin-2 gene (IL-2) do not easily explain the T cell specificity of IL-2 regulation. To seek additional determinants of cell type specificity, in vivo methodologies were employed to examine chromatin structure 5' and 3' of the 300 bp IL-2 proximal promoter/enhancer region. Restriction enzyme accessibility revealed that until stimulation the IL-2 proximal promoter/enhancer exists in a closed conformation in resting T and non-T cells alike. Within this promoter region, DMS and DNase I genomic footprinting also showed no tissue-specific differences prior to stimulation. However, DNase I footprinting of the distal -600 to -300 bp region revealed multiple tissue-specific and stimulation-independent DNase I hypersensitive sites. Gel shift assays detected T cell-specific complexes binding within this region, which include TCF/LEF or HMG family and probable Oct family components. Upon stimulation, new DNase I hypersensitive sites appeared in both the proximal and distal enhancer regions, implying that there may be a functional interaction between these two domains. These studies indicate that a region outside the established IL-2 minimal enhancer may serve as a stable nucleation site for tissue-specific factors and as a potential initiation site for activation-dependent chromatin remodeling.

Different developmental arrest points in RAG-2 -/- and SCID thymocytes on two genetic backgrounds: developmental choices and cell death mechanisms before TCR gene rearrangement

To analyze the early development of T cell precursors in the absence of TCR gene rearrangement, recombinase-activating gene-deficient (RAG-2 -/-) thymocytes were compared with thymocytes from SCID mice on the C.B-17 (BALB) and B6 genetic backgrounds. RAG-2 -/- thymocytes accumulate as quiescent cells with a heat-stable Ag (HSA)-positive CD25+ CD44- c-kit(low) phenotype, resembling normal cells just before selection for functional TCR beta-chain expression. CD44 and c-kit progressively down-regulate in the HSA+ subset, providing a background-independent and TCR-independent developmental clock. On this basis, compared with RAG-2 -/- thymocytes, SCID thymocytes 1) arrest at more heterogeneous, and generally earlier, stages; 2) accumulate to lower overall cell numbers; and 3) maintain higher populations of cycling and activated G1 cells, showing both increased responsiveness and increased cell death. B6-SCID thymocytes appear to die particularly early. Low levels of Fas were observed on "advanced" HSA+ SCID thymocytes but not on any RAG-2 -/- thymocytes, suggesting a potential difference in activation state or mechanism of death. In both RAG-2 -/- and SCID thymocytes, there are also two discrete subsets of HSA(low) CD25- CD44+ c-kit+ cells: a Sca-1+ CD44++ CD122- NK1.1- putative progenitor subset and an NK-like Sca-1- CD44+(+) CD122+ NK1.1+ subset. The absolute cell numbers in these HSA(low) subsets and the extent of NK cell differentiation, measured by perforin expression, are nearly constant in all the mutant strains analyzed, in contrast to the HSA+ CD25+ population, which was expanded in the RAG-2 -/-. Thus, the SCID thymocytes appear to undergo a normal generation but a premature death as compared with the RAG-2 -/- thymocytes.

Different developmental arrest points in RAG-2 -/- and SCID thymocytes on two genetic backgrounds: developmental choices and cell death mechanisms before TCR gene rearrangement

To analyze the early development of T cell precursors in the absence of TCR gene rearrangement, recombinase-activating gene-deficient (RAG-2 -/-) thymocytes were compared with thymocytes from SCID mice on the C.B-17 (BALB) and B6 genetic backgrounds. RAG-2 -/- thymocytes accumulate as quiescent cells with a heat-stable Ag (HSA)-positive CD25+ CD44- c-kit(low) phenotype, resembling normal cells just before selection for functional TCR beta-chain expression. CD44 and c-kit progressively down-regulate in the HSA+ subset, providing a background-independent and TCR-independent developmental clock. On this basis, compared with RAG-2 -/- thymocytes, SCID thymocytes 1) arrest at more heterogeneous, and generally earlier, stages; 2) accumulate to lower overall cell numbers; and 3) maintain higher populations of cycling and activated G1 cells, showing both increased responsiveness and increased cell death. B6-SCID thymocytes appear to die particularly early. Low levels of Fas were observed on "advanced" HSA+ SCID thymocytes but not on any RAG-2 -/- thymocytes, suggesting a potential difference in activation state or mechanism of death. In both RAG-2 -/- and SCID thymocytes, there are also two discrete subsets of HSA(low) CD25- CD44+ c-kit+ cells: a Sca-1+ CD44++ CD122- NK1.1- putative progenitor subset and an NK-like Sca-1- CD44+(+) CD122+ NK1.1+ subset. The absolute cell numbers in these HSA(low) subsets and the extent of NK cell differentiation, measured by perforin expression, are nearly constant in all the mutant strains analyzed, in contrast to the HSA+ CD25+ population, which was expanded in the RAG-2 -/-. Thus, the SCID thymocytes appear to undergo a normal generation but a premature death as compared with the RAG-2 -/- thymocytes.

A dynamic assembly of diverse transcription factors integrates activation and cell-type information for interleukin 2 gene regulation

The interleukin 2 (IL-2) gene is subject to two types of regulation: its expression is T-lymphocyte-specific and it is acutely dependent on specific activation signals. The IL-2 transcriptional apparatus integrates multiple types of biochemical information in determining whether or not the gene will be expressed, using multiple diverse transcription factors that are each optimally activated or inhibited by different signaling pathways. When activation of one or two of these factors is blocked IL-2 expression is completely inhibited. The inability of the other, unaffected factors to work is explained by the striking finding that none of the factors interacts stably with its target site in the IL-2 enhancer unless all the factors are present. Coordinate occupancy of all the sites in the minimal enhancer is apparently maintained by continuous assembly and disassembly cycles that respond to the instantaneous levels of each factor in the nuclear compartment. In addition, the minimal enhancer undergoes specific increases in DNase I accessibility, consistent with dramatic changes in chromatin structure upon activation. Still to be resolved is what interaction(s) conveys T-lineage specificity. In the absence of activating signals, the minimal IL-2 enhancer region in mature T cells is apparently unoccupied, exactly as in non-T lineage cells. However, in a conserved but poorly studied upstream region, we have now mapped several novel sites of DNase I hypersensitivity in vivo that constitutively distinguish IL-2 producer type T cells from cell types that cannot express IL-2. Thus a distinct domain of the IL-2 regulatory sequence may contain sites for competence- or lineage-marking protein contacts.

Joint pain

This article reviews the approach an internist might take with a patient with joint pain. It emphasizes aspects of the history and physical examination that help yield a diagnosis. The use of simple laboratory tests is reviewed, and common questions are answered. Some general management issues are discussed, although disease-specific therapy is beyond the scope of this article. It is hoped that this article will help an internist successfully diagnose most patients who present with joint pain.

Sequence of the gamma 2b membrane 3' untranslated region: polya site determination and comparison to the gamma 2a membrane 3' untranslated region

We present here the nucleotide sequence of the gamma 2b membrane 3' untranslated region as well as approximately 443 nucleotides of 3' flanking sequence. Although this region contains two potential polyadenylation hexanucleotides AATAAA (located 1328 and 1407 nucleotides downstream of the last membrane exon), it appears that only the first site directs polyadenylation of the mature mRNA. The first AATAAA is followed by several sequences which may influence its relative strength: the region downstream of this AATAAA is 44% T-rich and contains a pair of CAYTG sequences (4/5 match) which overlap two sequences which have a 6/8 match to the sequence YGTGTTYY. These sequences have been found in proximity to a large number of 3' ends [Gil and Proudfoot, Cell 49, 399-406 (1987); McLauchlan et al., Nucl. Acids Res. 13, 1347-1368. (1985); Berget, Nature 309, 179-182 (1984)]. The AATAAA site at position 1407 is not flanked by a T- or GT-rich sequence and is followed by a single CAYTG sequence (4/5 match) and a single YGTGTTYY sequence (6/8 match). The region downstream of the second AATAAA site also contains a sequence which has an 8/12 match with a sequence found in all heavy chain secreted 3' untranslated regions [Kobrin et al., Molec. Cell. Biol. 6, 1687-1697 (1986)]. Consistent with sequence comparisons between other regions of these two genes, the gamma 2b sequence has striking homology with the gamma 2a 3' untranslated region. A notable difference between gamma 2b and gamma 2a is the absence of an extensive array of GAA, GA, GGAA, and GGA repeats from the gamma 2b sequence. The GA repeats are postulated to form a stem loop structure in the gamma 2a 3' untranslated region; gamma 2b then would be missing the 5' half of the stem. Interestingly, neither the gamma 2b nor the gamma 2a 3' untranslated regions show large homologies to the mu, delta, gamma 3, or the alpha membrane 3' untranslated regions.

Spontaneous deletions in Ig heavy chain genes: flanking sequences influence splice site selection

The cell line G403.4.7, isolated as a spontaneous variant of the MPC-11 derived myeloma G403.4, produces a truncated gamma 2b HC protein, but no light chain (LC), and a single gamma 2b specific transcript of 2.4kb. This gamma 2b transcript consists of the VDJ and CH1 exons, the CH1 to Hinge (Hi) intervening sequence (IVS) and HI exon, part of the IVS between the two membrane exons M1 and M2, and most of the membrane 3' untranslated (UT) region. Even though the mature mRNA contains intronic sequences, it is abundant in the cytoplasm. Analysis of the gamma 2b genomic organization reveals that this unusual transcript results in part from two genomic deletions of 2.5kb and 588bp and in part from an altered splicing pattern. This altered splicing pattern is probably a consequence of the sequence alterations resulting from the genomic deletions. Analysis of these events provides some interesting insights into the mechanism of splice site selection and the evolution of introns and exons.

Studies of neutrophil production and turnover in grey collie dogs with cyclic neutropenia

12 grey collie dogs had cyclic neutropenia with the neutropenia recurring at 11.8+/-0.1-day intervals. The recovery from neutropenia was accompanied by a single wave of myeloid proliferation, an increase in marrow myeloid-labeling indices, and an increase in serum muramidase levels. After recovery from neutropenia during the period when blood neutrophils (PMN) were normal or increased, marrow myeloid precursors became scarce. The decline in marrow precursors and marrow PMN reserves heralded the recurrence of neutropenia. Neither diisopropyl fluorophosphate (DF(32)P) leukokinetic studies nor the rate of development of neutropenia suggested shortened PMN survival as a mechanism for the neutropenia. These studies indicate that the cyclic neutropenia is due to a regularly recurring failure in PMN production.