Insulin response to glucose and glucose tolerance following feeding in sheep

Clinical implications of ALDH1A1 and ALDH1A3 mRNA expression in melanoma subtypes

Aldehyde dehydrogenase (ALDH) activity is not only a valuable marker for cancer cells with stem-like features, but also plays a vital role in drug resistance and disease progression in many tumors including melanoma. However, the precise role of ALDH activity in patient prognosis remains unclear. In this study, using the Cancer Genome Atlas (TCGA) RNA-sequencing expression data, we analyzed gene expression of ALDH isozymes in melanoma tumors to define the expression patterns and the prognostic and predictive values of these enzymes. We found that ALDH1A1 and ALDH1A3 had both higher and broader expression ranges in melanoma patients, and that ALDH1A3 expression correlated with better overall survival in metastatic melanoma. Further, stratification of the TCGA cohorts by the mutational subtypes of melanoma specifically revealed that expression of ALDH1A3 correlated with better prognosis in metastatic BRAF-mutant melanoma while expression of ALDH1A1 correlated with better prognosis in BRAF wild-type melanoma. Gene set enrichment analysis (GSEA) of these cohorts identified upregulation in oxidative phosphorylation, adipogenesis, and fatty acid metabolism signaling in ALDH1A^lo patients, suggesting BRAF/MEK inhibitor resistance in that subset of patients. On the other hand, GSEA of ALDH1A3^hi cohorts revealed upregulation in glycolysis, hypoxia and angiogenesis, suggesting BRAF/MEK inhibitor sensitivity in that subset of patients. Gene expression analysis using pre-treatment tumor samples supports high ALDH1A3 expression before BRAF/MEK inhibitor treatment as predictive of better treatment response in BRAF-mutant melanoma patients. Our study provides evidence that high ALDH1A3 mRNA expression is not only a prognostic marker but also a predictive marker for BRAF/MEK inhibitor treatment response in BRAF-mutant metastatic melanoma patients.

In vivo changes in central and peripheral insulin sensitivity in a large animal model of obesity

Obesity disrupts homeostatic energy balance circuits leading to insulin resistance. Here we examined in vivo peripheral and central insulin sensitivity, and whether central insensitivity in terms of the voluntary food intake (VFI) response occurs within the hypothalamus or at blood-brain transfer level, during obesity and after subsequent weight loss. Sheep with intracerebroventricular (i.c.v.) cannulae were fed complete diet for 40 wk ad libitum (obese group) or at control level (controls). Thereafter, obese sheep were food restricted (slimmers) and controls fed ad libitum (fatteners) for 16 wk. Dual-energy x-ray absorptiometry (DEXA) measured total body fat, insulin analyses in blood and cerebrospinal fluid (CSF) assessed blood-brain transfer, i.v. glucose tolerance test (GTT) and insulin tolerance test (ITT) measured peripheral insulin sensitivity, and VFI responses to icv insulin assessed intrahypothalamic sensitivity. Insulinemia was higher in obese than controls; plasma insulin correlated with DEXA body fat and CSF insulin. Insulinemia was higher in fatteners than slimmers but ratio of CSF to plasma insulin correlated only in fatteners. Plasma glucose baseline and area under the curve were higher during GTT and ITT in obese than controls and during ITT in fatteners than slimmers. GTT and ITT glucose area under the curve correlated with DEXA body fat. VFI decreased after i.c.v. insulin, with response magnitude correlating negatively with DEXA body fat. Overall, insulin resistance developed first in the periphery and then within the brain, thereafter correlating with adiposity; central resistance in terms of VFI response resulted from intrahypothalamic insensitivity rather than impaired blood-brain transfer; modest weight loss improved peripheral but not central insulin sensitivity and induced central hypoinsulinemia.

Photoperiod regulates clock gene rhythms in the ovine liver

To investigate the photoperiodic entrainment of peripheral rhythms in ruminants, we studied the expression of clock genes in the liver in the highly seasonal Soay sheep. Animals were kept under long (LD 16:8) or short photoperiod (LD 8:16). Daily rhythms in locomotor activity were recorded, and blood concentrations of melatonin and cortisol were measured by RIA. Per2, Bmal1, and Cry1 gene expression was determined by Northern blot analyses using ovine RNA probes in liver collected every 4h for 24h. Liver Per2 and Bmal1, but not Cry1, expression was rhythmic in all treatments. Under long days, peak Per2 expression occurred at end of the night with a similar timing to Bmal1, whereas, under short days the Per2 maximum was in the early night with an inverse pattern to Bmal1. There was a photoperiodxtime interaction for only Per2 (P < 0.001). The 24-h pattern in plasma cortisol matched the observed phasing of Per2 expression, suggesting that it may act as an endocrine entraining factor. The clock gene rhythms in the peripheral tissues were different in timing compared with the ovine suprachiasmatic nucleus (SCN, central pacemaker) and pars tuberalis (melatonin target tissue), and the hepatic rhythms were of lower amplitude compared with photoperiodic rodents. Thus, there are likely to be important species differences in the way the central and peripheral clockwork encodes external photoperiod.

Effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin in sheep

The effects of moderate hyperthyroidism and time relative to feeding on tissue responsiveness to insulin were determined in four sheep using a hyperinsulinemic euglycemic clamp procedure, because thyroid hormones have glucoregulatory function in ruminants and non-ruminant animals. The sheep were fed alfalfa hay cubes and corn-based concentrates. They were intravenously injected in turn with saline (control treatment) and then with triiodothyronine (1.5 nmol d(-1); T3 treatment) once daily for 23 days for each treatment. The glucose clamp procedure was performed at four different times relative to feeding (before, during and after feeding) in both treatments. Insulin was intravenously infused at a constant rate of 6.0 mU (kgxmin)(-1) for 2 h and a glucose solution was infused to maintain euglycemia. Plasma T3 concentrations were higher (P=0.0001) for the T3 treatment than for the control treatment (4.0 and 1.3 nmol l(-1), respectively). For the glucose clamp procedure, glucose infusion rates were greater (P=0.0001) for the T3 treatment than for the control treatment, and were greater (P<0.05) during feeding than before feeding and after the end of feeding, but no interaction was detected. In conclusion, tissue responsiveness to insulin in sheep was independently enhanced by moderate hyperthyroidism induced by intravenous T3 injection and feeding.

Effect of feed intake and dietary vitamin A levels on sheep performance

A study was conducted on 20 "Rahmani" male lambs of 16 kg body weight fed on normal feed level and high vitamin A level (NF-HV); normal feed level and normal vitamin A level (NF-NV); low feed level and high vitamin A level (LF-HV) or low feed level and normal vitamin A level (LF-NV) till slaughter weight of 35-40 kg. Average daily gains of lambs were 211, 148, 117 and 87 g for the NF-HV, NF-NV, LF-HV and LF-NV groups, respectively. The corresponding feed conversions were 4.3, 5.9, 5.0 and 6.4 kg DM/kg gain. Raising feed intake and vitamin A level enhanced nutrients digestibility and nitrogen balance. Rumen liquor reflected higher pH value in animals fed higher intake (NF) in the first two diets. Both feed intake and vitamin A levels enhanced volatile fatty acids and ammonia concentrations in the rumen liquor. Feed intake and vitamin A levels positively affected haemoglobin content, packed cell volume, glucose, urea, total protein, vitamin A, insulin, cholesterol, phospholipids, glutamate oxaloacetate and glutamate pyruvate transaminases and alkaline phosphatase in blood Vitamin A, insulin, cholesterol and phospholipids in blood increased gradually over the experimental period. Dressing percentages were 56.2, 49.6, 49.1 and 44.6% for the experimental groups, respectively. Liver content of glycogen and vitamin A increased with increasing feed intake and vitamin A levels. It is concluded that higher levels of vitamin A supplementation (than usually recommended) is required during fattening of lambs. Low energy and normal vitamin A levels are not recommended in lambs feeding.

Adrenergic modulation of pancreatic glucagon and insulin secretion in goats

Five goats were used to investigate adrenergic influences on the secretion of both glucagon and insulin. The secretion of glucagon was augmented via alpha-adrenergic stimulation. The secretion of insulin was enhanced by stimulation of beta-adrenergic receptors and inhibited by alpha-adrenergic stimulation.