Lymphatic absorption, metabolism, and excretion of a therapeutic peptide in dogs and rats.

The objective of the current study was to evaluate the mechanism of absorption and metabolism of a PEGylated peptide, MRL-1 (46 kDa), after s.c. dosing in dogs and rats. Thoracic lymph duct-cannulated (LDC) dog and rat models were developed that allowed continuous collection of lymph for up to 8 days. When [(3)H]MRL-1 was administered s.c. to LDC dogs, ∼73% of the administered radioactivity was recovered in pooled lymph over a period of 120 hours, suggesting that lymphatic uptake is the major pathway of s.c. absorption for this peptide. In agreement with these data, the systemic exposure of radioactivity related to [(3)H]MRL-1 in LDC dogs was decreased proportionately when compared with that in noncannulated control dogs. After i.v. dosing with [(3)H]MRL-1 in LDC dogs, 20% of the administered radioactivity was recovered in pooled lymph over 168 hours, suggesting some level of recirculation of radioactivity related to [(3)H]MRL-1 from the plasma compartment into the lymphatic system. Experiments conducted in the LDC rat model also resulted in similar conclusions. Analysis of injection site s.c. tissue showed significant metabolism of [(3)H]MRL-1, which provides an explanation for the <100% bioavailability of therapeutic proteins and peptides after s.c. dosing. After s.c. dosing, the major circulating components in plasma were the parent peptide and the PEG-linker [(3)H]MRL-2. The metabolism profiles in lymph were similar to those in plasma, suggesting that the loss of peptide was minimal during lymphatic transport. After i.v. dosing in rats, [(3)H]MRL-1 was metabolized and excreted primarily in the urine as metabolites.

Lymphatic transport and catabolism of therapeutic proteins after subcutaneous administration to rats and dogs.

The mechanism underlying subcutaneous absorption of macromolecules and factors that can influence this process were studied in rats using PEGylated erythropoietins (EPOs) as model compounds. Using a thoracic lymph duct cannulation (LDC) model, we showed that PEGylated EPO was absorbed from the subcutaneous injection site mainly via the lymphatic system in rats, which is similar to previous reports in sheep. After subcutaneous administration, the serum exposure was reduced by ∼70% in LDC animals compared with that in the control animals, and most of the systemically available dose was recovered in the lymph. In both LDC and intact rats, the total radioactivity recoveries in excreta after subcutaneous administration were high (70-80%), indicating that catabolism, not poor absorption, was the main cause for the observed low bioavailability (30-40%). Moreover, catabolism of PEGylated EPO was found with both rat subcutaneous tissue homogenate and lymph node cell suspensions, and a significant amount of dose-related breakdown fragments was found in the lymph of LDC rats. In addition, the bioavailability of PEGylated EPOs was shown to be 2- to 4-fold lower in "fat rats," indicating that physiologic features pertinent to lymphatic transport can have a profound impact on subcutaneous absorption. Limited studies in dogs also suggested similar subcutaneous absorption mechanisms. Collectively, our results suggest that the lymphatic absorption mechanism for macromolecules is probably conserved among commonly used preclinical species, e.g., rats and dogs, and that mechanistic understanding of the subcutaneous absorption mechanism and associated determinants should be helpful in biologic drug discovery and development.

Management of a gunshot wound in a mare.

A 5-year-old, Quarter horse mare was treated for severe cellulitis secondary to a gunshot wound near the right humerus. The bullet was not retrieved due to the risk of damaging the radial nerve or elbow joint. Despite the presence of the bullet, the mare resumed athletic soundness once the infection had resolved.

Analysis of biological phenotypes from 42 patients with inherited factor VII deficiency: can biological tests predict the bleeding risk?

BACKGROUND AND OBJECTIVES: Inherited factor VII (FVII) deficiency is a rare bleeding disorder characterized by a poor relationship between reported FVII clotting activity (FVII:C) and bleeding tendency. Our study was aimed at defining biological parameters that are possibly predictive for bleeding risk in this condition. DESIGN AND METHODS: Forty-two FVII-deficient patients (FVII:C <30%) were classified into two opposite clinical groups defined as severe and non-or-mild bleeders. For each patient, plasma samples were collected and then investigated for FVII:C (using a sensitive method and human recombinant thromboplastin as the reagent), FVII antigen, activated FVII coagulant activity (FVIIa:C) and the free-form of tissue factor pathway inhibitor. RESULTS: None of these tests could be used as highly accurate predictors of bleeding. Nevertheless, both FVII:C and FVIIa:C differed significantly between the two clinical groups. Using ROC-curve analysis, two critical values of 8% and 3mIU/mL for FVII:C and FVIIa:C, respectively, could be proposed to discriminate between severe bleeders and non-or-mild bleeders. INTERPRETATION AND CONCLUSIONS: A highly accurate diagnostic test for predicting bleeding tendency in inherited FVII deficiency still eludes definition, highlighting the fact that factors other than FVII itself interfere with the expression of bleeding phenotypes in this condition. Nevertheless, potential critical values using sensitive FVII:C and FVIIa:C methods may be useful in clinical laboratories for FVII-deficient patients. Those patients with FVII:C levels higher than 8% FVII:C or FVIIa:C higher than 3 mIU/mL, with no other hemostatic defect, seem to have a minimal risk of severe bleeding. Extended clinical studies are needed to support these findings.

Discharge properties of group III and IV muscle afferents.

Stimulation of group III and IV muscle afferents has been shown to have important reflex effects on both the somatic and autonomic nervous systems. These include an inhibitory effect on alpha motoneurones, an excitatory effect on gamma motoneurones and an excitatory effect on the sympathetic nervous system. The purpose of this review is to describe the mechanical and metabolic stimuli that discharge group III and IV muscle afferents. Particular attention will be paid to the responses of these afferents to dynamic exercise induced by electrical stimulation of the mesencephalic locomotor region.