Inhibition of factor IXa by the pegnivacogin system during cardiopulmonary bypass: a potential substitute for heparin. A study in baboons.

OBJECTIVES: Heparin and protamine are standard for anticoagulation and reversal for cardiopulmonary bypass (CPB). The REGADO biosciences protocol 1 (REG1) anticoagulant system, consisting of the Factor IXa (FIXa)-inhibitor pegnivacogin and its reversal agent (anivamersen), has been studied in patients undergoing coronary catheterization and in CPB in sheep and pigs. Prior to first human use in CPB, we wanted to test the safety and efficacy of REG1 in a primate model. METHODS: Fourteen baboons undergoing 2 h of CPB followed by 1 h of reperfusion were studied. Three received heparin/protamine and 11 received 1 of 2 doses of pegnivacogin followed by anivamersen. Thrombin-generating capacity was tested in additional in vitro experiments. RESULTS: Targeted drug levels and near-complete FIXa inhibition were achieved. Bypass was run uneventfully in all animals without any clotting in the circuit and bleeding was minimal in the two groups. However, in contrast to heparin-treated baboons, those receiving pegnivacogin/anivamersen displayed thrombi in the bypass cannulae upon cannulation and kidney cortical infarcts. Inter-species comparisons revealed that in the presence of high levels of FIXa inhibition, tissue factor-mediated thrombin generation in baboons was much higher than that in other species. CONCLUSIONS: These data highlight the limitations of the baboon model for assessing factor-specific coagulation inhibitors during CPB. The justification for Phase 1 human studies using REG1 for CPB is unclear.

Comparison of energy balance in two inbred strains of rats: Fischer F344 prone to obesity and Lou rats resistant to obesity.

This study aimed to compare energy balance, metabolic profiles and body composition between two inbred strains of rats (F344 and Lou) submitted to a self-selecting macronutrient. During the 3 weeks of experiment, the two strains did not differ significantly for their total energy intake; males: F344 = 5875.4 +/- 171.4 kJ, Lou = 5619.2 +/- 349.4 kJ; and females: F344 = 4058.8 +/- 118.7 kJ, Lou = 3864.4+/-166.4 kJ. However, F344 rats showed a higher weight gain, and percentage of total fat tissue, together with a lower percentage of carcass weight than Lou rats regardless of sex. The percentages of each macronutrient revealed a lower preference of protein for F344 males and the opposite in females for CHO. The thermogenic activity measured in interscapular brown adipose tissue was lower in Fischer than in Lou while the reverse was observed for leptinemia and insulinemia. These results indicate that the mechanism responsible for the regulation of body composition observed in Lou rats takes place very early in life and attest the interest in this strain for studying the features of resistance to obesity.

Comparison of fat storage between Fischer 344 and obesity-resistant Lou/C rats fed different diets.

OBJECTIVE: We aimed to characterize further the Lou/C (LOU) and Fischer 344 (F344) rat strains for nutritional traits to validate their use as contrasting strains for molecular genetic studies. RESEARCH METHODS AND PROCEDURES: Five batches of LOU and F344 rats were used to measure caloric intake, weight gain, and body composition when fed a chow diet, a self-selection diet (together with the study of preferences for macronutrients), hypercaloric diets, and a chow diet in a cold environment. RESULTS: Despite a higher caloric intake when fed a chow diet, LOU rats showed a lower weight gain, final body weight, and percentage of fat tissue, together with a higher percentage of carcass weight, than F344 rats. When fed a self-selection diet, LOU males ingested less protein and more fat than F344 males, and the reverse was observed for females. In this condition, feed efficiency was reduced in LOU but increased in F344 rats compared with the chow diet. Diet-induced obesity was observed in F344 rats but not in LOU rats fed hypercaloric diets. In a cold environment, both LOU and F344 rats displayed an increased percentage of brown adipose tissue compared with control groups, together with a higher caloric intake. DISCUSSION: The study shows robust nutritional differences between the LOU rat, a lean strain with a low feed efficiency and resistant to diet-induced obesity, and the contrasting F344 rat strain. It also shows the interest in these strains for studying the genetic components of resistance to obesity.