Recombinant rat and mouse growth hormones: risk assessment of carcinogenic potential in 2-year bioassays in rats and mice.

Recombinant rat growth hormone (rrGH) and recombinant mouse growth hormone (rmGH) were developed to evaluate the potential carcinogenicity of each biologically active growth hormone (GH) as assessed in the respective species. Biological activities of rrGH and rmGH were demonstrated by showing an increase in body weight gain and serum levels of insulin-like growth factor-1 (IGF-1) in hypophysectomized rats receiving daily sc injections for 6 days. With the exception of pharmacologically mediated weight gain, rrGH and rmGH had no adverse effects in 5-week oral toxicity studies and no production of anti-recombinant GH antibodies. The high doses selected for the carcinogenicity studies provided systemic exposures of GH up to approximately 10-fold over basal levels. In the 105-week mouse carcinogenicity study, daily sc injections of rmGH at 0.1, 0.2, or 0.5 mg/kg/day were well tolerated and had no effects on survival or incidence of tumors. In the 106-week rat carcinogenicity study, daily sc injections of rrGH at 0.2, 0.4, or 0.8 mg/kg/day had a favorable effect on longevity in female rats administered 0.4 or 0.8 mg/kg/day, an increased weight gain in females and males, and no increase in the incidence of tumors. The absence of carcinogenic effects of recombinant GH administered daily for 2 years to rodents was consistent with publications of clinical experience, indicating a lack of convincing evidence for an increased risk of cancer in children receiving human recombinant GH replacement therapy.

Systemic pan-AMPK activator MK-8722 improves glucose homeostasis but induces cardiac hypertrophy.

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy homeostasis in eukaryotes. Despite three decades of investigation, the biological roles of AMPK and its potential as a drug target remain incompletely understood, largely because of a lack of optimized pharmacological tools. We developed MK-8722, a potent, direct, allosteric activator of all 12 mammalian AMPK complexes. In rodents and rhesus monkeys, MK-8722-mediated AMPK activation in skeletal muscle induced robust, durable, insulin-independent glucose uptake and glycogen synthesis, with resultant improvements in glycemia and no evidence of hypoglycemia. These effects translated across species, including diabetic rhesus monkeys, but manifested with concomitant cardiac hypertrophy and increased cardiac glycogen without apparent functional sequelae.

Use of a radioreceptorassay (RRA) for human luteinizing hormone/chorionic gonadotropin (hLH/CG) for detection of early pregnancy and estimation of time of ovulation in macaques.

A radioreceptorassay (RRA) for macaque luteinizing hormone (LH)/chorionic gonadotropin (CG) was adapted from the clinical RRA for human LH/CG, Biocept-G™, for the purposes of detection of pregnancy prior to day 20 of gestation and for estimation of the time of ovulation in macaques. The 90-min assay procedure was simple, accurate, and reliable. Seventy-five rhesus monkeys (Macaca mulatta) and 20 crab-eating monkeys (Macaca fascicularis) were tested for the presence of CG in the serum on estimated days 17-20 of pregnancy. Of a total of 160 tests, four false negative and 0 false positive tests were obtained, for an accuracy of 97.5%. The preovulatory LH peak was detected in 19 rhesus monkeys by semiquantitative RRA of LH/CG. Ovulation was confirmed in these 19 animals by the presence of a fresh corpus luteum at laparotomy 2-10 days after ovulation, collection of an embryo, pregnancy, or subsequent cycle history. The short, simple assay procedure and the low inter-and intraassay coefficients of variation (7.3 and 3.7%, respectively) allow use of this assay in an economical, predictive, as well as retrospective, capacity for estimation of the time of ovulation in rhesus monkeys. The sensitivity, reliability, species nonspecificity, simplicity, and rapidity of performance of this RRA for LH/CG are features which add up to a useful new management tool for breeding macaques for research purposes.

Characterization of the exocrine pancreas in the male Zucker diabetic fatty rat model of type 2 diabetes mellitus following 3 months of treatment with sitagliptin.

Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor-based incretin therapy intended for the treatment of type 2 diabetes mellitus (T2DM), has not been linked to adverse effects on the pancreas in prospective clinical trials or in nonclinical toxicology studies. To further assess potential pancreatic effects, sitagliptin was studied in the male Zucker diabetic fatty (ZDF) rat model of T2DM. Following 3 months of oral dosing with vehicle, or sitagliptin at doses 3- to 19-fold above the clinically therapeutic plasma concentration, which increased active plasma glucagon-like peptide-1 levels up to approximately 3-fold, or following 3 months of oral dosing with metformin, a non-incretin-based reference T2DM treatment, the pancreas of male ZDF rats was evaluated using qualitative and quantitative histopathology techniques. In the quantitative evaluation, proliferative index was calculated in exocrine pancreatic ducts and ductules using computer-based image analysis on sections stained by immunohistochemistry for cytokeratin (a cytoplasmic epithelial cell marker) and Ki-67 (a nuclear marker of recent cell division). Relative to controls, sitagliptin treatment did not alter disease progression based on detailed clinical signs and clinical pathology assessments. Sitagliptin treatment did not result in pancreatitis or any adverse effect on the pancreas based on a qualitative histopathology evaluation. Proliferative index did not increase with sitagliptin treatment based on quantitative assessment of more than 5000 sections of pancreas, where control group means ranged from 0.698-0.845% and sitagliptin-treated group means ranged from 0.679-0.701% (P = .874). Metformin treatment was similarly evaluated and found not to have adverse effects on pancreas.

Spontaneous epithelioid hemangiosarcoma in a rhesus monkey (Macaca mulatta).

Epithelioid hemangiosarcoma is a rare malignant endothelial neoplasia with a unique, predominantly epithelioid morphology. A 4-y-old rhesus monkey from our laboratory had multiple neoplastic nodules in a digit, limb skin, hindlimb muscle, and visceral organs including lung, heart, and brain. The nodules were composed of pleomorphic, polygonal, epithelioid, neoplastic cells that were arranged in sheets, nests, and cords and supported by variably dense fibrovascular connective tissue. The morphologic features of this tumor were predominantly epithelioid. However, some regions contained cystic spaces, clefts, and channel-like structures, all of which were lined with morphologically distinct neoplastic endothelial cells. These neoplastic cells, with or without epithelioid morphology, were positive immunohistochemically for CD31, factor VIII-related antigen, and vimentin. The presence of multiple metastatic nodules, high mitotic rate, and extensive Ki67-positive staining were consistent with malignancy. This report is the first description of epithelioid hemangiosarcoma in a rhesus monkey.