Reduced Serum IGF‐1 Associated With Hepatic Osteodystrophy Is a Main Determinant of Low Cortical but Not Trabecular Bone Mass

Hepatic osteodystrophy is multifactorial in its pathogenesis. Numerous studies have shown that impairments of the hepatic growth hormone/insulin‐like growth factor‐1 axis (GH/IGF‐1) are common in patients with non‐alcoholic fatty liver disease, chronic viral hepatitis, liver cirrhosis, and chronic cholestatic liver disease. Moreover, these conditions are also associated with low bone mineral density (BMD) and greater fracture risk, particularly in cortical bone sites. Hence, we addressed whether disruptions in the GH/IGF‐1 axis were causally related to the low bone mass in states of chronic liver disease using a mouse model of liver‐specific GH‐receptor (GHR) gene deletion (Li‐GHRKO). These mice exhibit chronic hepatic steatosis, local inflammation, and reduced BMD. We then employed a crossing strategy to restore liver production of IGF‐1 via hepatic IGF‐1 transgene (HIT). The resultant Li‐GHRKO‐HIT mouse model allowed us to dissect the roles of liver‐derived IGF‐1 in the pathogenesis of osteodystrophy during liver disease. We found that hepatic IGF‐1 restored cortical bone acquisition, microarchitecture, and mechanical properties during growth in Li‐GHRKO‐HIT mice, which was maintained during aging. However, trabecular bone volume was not restored in the Li‐GHRKO‐HIT mice. We found increased bone resorption indices in vivo as well as increased basal reactive oxygen species and increased mitochondrial stress in osteoblast cultures from Li‐GHRKO and the Li‐GHRKO‐HIT compared with control mice. Changes in systemic markers such as inflammatory cytokines, osteoprotegerin, osteopontin, parathyroid hormone, osteocalcin, or carboxy‐terminal collagen cross‐links could not fully account for the diminished trabecular bone in the Li‐GHRKO‐HIT mice. Thus, the reduced serum IGF‐1 associated with hepatic osteodystrophy is a main determinant of low cortical but not trabecular bone mass. © 2017 American Society for Bone and Mineral Research.     

Balloon‐occluded retrograde transvenous obliteration for recurrent fundal gastric variceal bleeding in an adolescent

Gastric variceal bleeding is associated with high morbidity and mortality. Balloon‐occluded retrograde transvenous obliteration is a relatively new treatment used to control bleeding gastric varices that involves transvenous sclerosis of gastric varices through a spontaneous gastrorenal shunt. Here, we report on a 14‐yr‐old patient that underwent balloon‐occluded retrograde transvenous obliteration for refractory bleeding fundal varices in the setting of esophageal varices and cirrhosis, which did not respond to medical management or endoscopic injection. This case report serves as a reminder that balloon‐occluded retrograde transvenous obliteration can successfully control fundal variceal bleeding in pediatric patients and may serve as a bridge to liver transplantation.     

Effects of electromagnetic stimuli on bone and bone cells in vitro: Inhibition of responses to parathyroid hormone by low-energy low-frequency fields

Low-energy electromagnetic fields pulsed at frequencies of 10-90 Hz significantly increase healing of chronic fracture nonunions in man. These fields are effective at tissue current levels several orders of magnitude lower than those required for transmembrane depolarization of normal cells. We have examined the effects of two clinically used pulsed electromagnetic fields on cultures of the osteoblast-like mouse bone cell line MMB-1. Both fields significantly reduced cellular production of cAMP in response to parathyroid hormone and osteoclast activating factor. Neither basal nor fluoride-activated levels of adenylate cyclase were altered in membranes from cells cultured in the fields; however, the same membrane preparations exhibited markedly inhibited responses to parathyroid hormone. The fields blocked the inhibitory effects of the hormone on collagen synthesis by MMB-1 cells. However, there was no effect on the inhibition of collagen synthesis by 1,25-dihydroxyvitamin D(3), which is believed to act primarily by a nuclear, rather than by a membrane-dependent, mechanism. No significant differences were noted between effects of the two fields, one generating continuous pulse trains (72 Hz) and the other generating recurrent bursts (15 Hz) of shorter pulses. We hypothesize that these field effects are mediated primarily at the plasma membrane of osteoblasts, either by interference with hormone-receptor interactions or by blocking of receptor-cyclase coupling in the membrane. These responses occurred with induced extracellular fields of 1 mV/cm or less, even though transmembrane potential gradients are typically 10(5) V/cm.     

Ectopic Production of the Isolated Beta Subunit of Human Chorionic Gonadotropin

A material similar to the beta subunit of human chorionic gonadotropin (hCG-β) was detected in serum (300 ng/ml) and tumor extract from a 75-yr-old man with pancreatic adenosquamous carcinoma. This material was indistinguishable from hCG-β in three different types of radioimmunoassay that displayed widely varying reactions with glycoprotein trophic hormones and their subunits. In gel chromatography there appeared to be heterogeneity of the serum beta-like immunoactivity, including one component that coeluted with standard hCG-β tracer and another immunologically indistinguishable component that displayed a slightly lower elution volume. Neither complete human chorionic gonadotropin (hCG) nor its alpha subunit was detected in radioimmunoassays of serum, before or after fractionation, or in tumor extract. The absence of complete hCG was confirmed in a gonadotropin bioassay sensitive to 15 ng of hCG, which showed no bioactivity in serum or tumor extract containing 450 and 90 ng of hCG-β, respectively. This case probably represents the first demonstration of isolated polypeptide subunit production of ectopic origin and suggests that hCG-β, as well as other subunits, may prove useful as cancer markers.     

Studies in vivo and in vitro on an abnormality in the metabolism of C3 in a patient with increased susceptibility to infection

In a patient with increased susceptibility to infection, lowered serum C3 concentration, and continuously circulating C3b, it was shown that purified (125)I-labeled C3 was converted to labeled C3b shortly after intravenous administration. The fractional catabolic rate of C3 was approximately five times normal at 10% of the plasma pool per hr. The synthesis rate and pool distribution of C3 were normal. Despite this evidence of C3 instability in vivo, no accelerated inactivation of C3 was found in vitro. Similarly, no free proteolytic activity could be detected in the patient's serum, and serum concentrations of known protease inhibitors were normal.Complement-mediated functions, which were markedly deficient in the patient's serum, could be restored partially or completely by the addition of a 5-6S heat-labile beta pseudoglobulin from normal serum. The C3 proinactivator, which has these physicochemical characteristics, was also shown to be either absent or nonfunctional in the patient's serum. An unidentified 6S beta pseudoglobulin to which a monospecific antiserum was available was not detectable in the patient's serum. This last protein appeared not to be a complement component, nor was it the C3 inactivator or proinactivator. Finally, the substance or substances necessary for the conversion of C3b to C3c were missing from the patient's serum.The administration of 500 ml of normal plasma to the patient corrected all of his abnormalities partially or completely for as long as 17 days. The changes in C3 were dramatic; serum concentration rose from 8 to 70 mg/100 ml, and C3b could no longer be detected. A second metabolic study during this normalization period showed a decrease in fractional catabolic rate toward normal.The patient's histamine excretion was constantly elevated but increased further after a warm shower and after receiving normal plasma; at both times he had urticaria. These observations were consistent with the endogenous production of C3a and the resulting histamine release from mast cells. The inactivating mechanism for C3a was apparently intact in the patient's serum.The difference in the electrophoretic mobilities of C3b and C3c was shown as well as the electrophoretic heterogeneity of C3c. Suggestive evidence was also presented that the form of C3 with an activated combining site for red cells, previously postulated by others, is a transient C3 conversion product with an electrophoretic mobility slower than that of C3 on agarose electrophoresis.     

Evaluation of a stable gonadotropin-releasing hormone analog in mice for the treatment of endocrine disorders and prostate cancer

Gonadotropin-releasing hormone (GnRH) receptor agonists have wide clinical applications including the treatment of prostate cancer and endocrine disorders. However, such agonists are characterized by poor pharmacokinetic properties, often requiring repeated administration or special formulations. Therefore, the development of novel peptide analogs with enhanced in vivo stability could potentially provide therapeutic alternatives. The pharmacological evaluation of a bioactive peptide [Des-Gly1?,Tyr?(OMe),D-Leu?,Aze-NHEt?]GnRH, analog 1, is presented herein and compared with leuprolide. Peptide stability was evaluated using mouse kidney membrane preparations, followed by a liquid chromatography-tandem mass spectrometry-based approach that afforded identification and quantification of its major metabolites. The analog was significantly more stable in vitro in comparison with leuprolide. In vitro and in vivo stability results correlated well, encouraging us to develop a clinically relevant pharmacokinetic mouse model, which facilitated efficacy measurements using testosterone as a biomarker. Analog 1, an agonist of the GnRH receptor with a binding affinity in the nanomolar range, caused testosterone release in mice that was acutely dose-dependent, an effect blocked by the GnRH receptor antagonist cetrorelix. Repeated dosing studies in mice demonstrated that analog 1 was well tolerated and had potency similar to that of leuprolide, based on plasma and testis testosterone reduction and histopathological findings. Analog 1 also shared with leuprolide similar significant antiproliferative activity on androgen-dependent prostate cancer (LNCaP) cells. On the basis of pharmacokinetic advantages, we expect that analog 1 or analogs based on this new design will be therapeutically advantageous for the treatment of cancer and endocrine disorders.     

The electrophysiological effects of ouabain on sinus node and atrium in man.

Electrophysiological studies were performed in 16 patients before and 30 min after intravenous administration of ouabain (0.1 mg/kg). P-A interval (mean+/-SEM) was 40+/-2.1 ms before and 44+/- 1.5 ms after ouabain (P less than 0.001). Atrial effective and functional refractory periods (ERP and FRP) were measured in all patients during sinus rhythm and during driving at equivalent paced rates in 12 patients. The mean atrial ERP and FRP during sinus rhythm were, respectively, 244+/-10.5 and 307+/-11.0 ms before and 253+/-9.7 and 318+/-11.4 ms after infusion of ouabain (NS). Mean atrial ERP and FRP during driving were, respectively, 231+/-15.3 and 264+/-14.9 ms before and 266+/-18.6 and 296+/-19.7 ms after ouabain (P less than 0.01 and P less than 0.01). Mean sinus cycle length and sinus recovery times were, respectively, 887+/-31.2 and 1,113+/-38.7 ms before and 905+/-38.2 and 1,008+/-30.7 ms after infusion of ouabain (NS and P less than 0.005). Calculated sinoatrial conduction times before and after ouabain were 90+/-6.8 and 110+/-8.5 ms, respectively (P less than 0.005). In summary, ouabain produced depression of intraatrial conduction as manifested by increase in P-A interval and atrial effective and functional refractory periods. Ouabain significantly increased calculated sinoatrial conduction time without significant effect on spontaneous sinus cycle length.