A model to explore the interaction between muscle insulin resistance and beta-cell dysfunction in the development of type 2 diabetes

Type 2 diabetes is a polygenic disease characterized by defects in both insulin secretion and insulin action. We have previously reported that isolated insulin resistance in muscle by a tissue-specific insulin receptor knockout (MIRKO mouse) is not sufficient to alter glucose homeostasis, whereas beta-cell-specific insulin receptor knockout (betaIRKO) mice manifest severe progressive glucose intolerance due to loss of glucose-stimulated acute-phase insulin release. To explore the interaction between insulin resistance in muscle and altered insulin secretion, we created a double tissue-specific insulin receptor knockout in these tissues. Surprisingly, betaIRKO-MIRKO mice show an improvement rather than a deterioration of glucose tolerance when compared to betaIRKO mice. This is due to improved glucose-stimulated acute insulin release and redistribution of substrates with increased glucose uptake in adipose tissue and liver in vivo, without a significant decrease in muscle glucose uptake. Thus, insulin resistance in muscle leads to improved glucose-stimulated first-phase insulin secretion from beta-cells and shunting of substrates to nonmuscle tissues, collectively leading to improved glucose tolerance. These data suggest that muscle, either via changes in substrate availability or by acting as an endocrine tissue, communicates with and regulates insulin sensitivity in other tissues.     

High-affinity, calcium-stimulated ATPase in brush border membranes of the human term placenta

ATPase activity which is stimulated by submicromolar concentrations of calcium (Ca2+) was identified in human placental microvillous brush border membranes. The high-affinity enzyme has an apparent K0.5 for free Ca2+ of 18.3 +/- 3.7 nM and a Vmax of 233.0 +/- 30.0 nmol/min/mg protein. Studies using trans-1,2-diaminocyclohexane-N,N,N1,N1-tetraacetic acid (CDTA) show that this enzyme requires submicromolar concentrations of Mg2+ for maximal activity, but that it appears to have a low basal activity in the absence of this cation. The high-affinity Ca2+-ATPase was unaffected by up to 100 microM concentrations of vanadate, but was sensitive to trifluoperazine inhibition (I50 less than 50 microM). It was not found to be stimulated by the addition of up to 10 micrograms calmodulin, but this lack of effect may be related to the endogenous calmodulin content of the membrane preparation. A low-affinity, non-specific divalent cation ATPase was also identified in this membrane preparation. In contrast to the high-affinity enzyme, it has an apparent K0.5 for calcium of 99.7 +/- 22.1 microM, and a Vmax of 1.54 +/- 0.17 mumol/min/mg protein. The characteristics of the high-affinity Ca2-ATPase are similar to those of other Ca2+- ATPases known to transport and regulate intracellular calcium concentrations in other tissues. By analogy, we suggest that the high-affinity Ca2+-ATPase described here could play an important role in cellular calcium homeostasis in the human placenta.     

Human placental lipid peroxidation. Some characteristics of the NADPH-supported microsomal reaction

1. The evidence presented in this paper indicates the existence of NADPH-supported lipid peroxidation in human placental microsomes. Thiobarbituric acid assay was used to estimate quantitatively lipid peroxidation. 2. Several biochemical characteristics of the reaction were examined. Maximal lipid peroxidation occurred at pH 7.4 and at a protein concentration of approx. 0.2 mg microsomal protein/ml. The presence of NADPH and chelated iron was required. The reaction was linear up to 5 min and did not exhibit an initial lag phase. 3. Under optimal assay conditions, the rate of lipid peroxidation ranged from 2 to 6 nmol malondialdehyde formed/min/mg protein in different preparations of placental microsomes. 4. Inconclusive results were obtained when assays were performed in the presence of scavengers of reactive oxygen species. 5. Marked inhibition in the malondialdehyde accumulation was observed when phosphate buffer was added to the incubation media. 6. This inhibitory effect appeared to be due to the removal of chelated iron from the system and not due to interference with the electron transport mechanism.     

Distichiasis: An update on etiology,treatment and outcomes

Distichiasis, an extra row of eyelashes emerging from meibomian gland orifices, occurs due to the metaplastic transition of sebaceous glands into the pilosebaceous unit. It can present congenitally, such as in lymphedema distichiasis syndrome, or secondary to acquired conditions, such as cicatrizing conjunctivitis, trachoma. This review summarizes the etiology of distichiasis, its presentation, the evolution of various surgical techniques, and their outcomes in human and animal eyes. The published literature has focused on the different treatment modalities and their outcomes; the etiopathogenesis of this condition remains elusive. Truncating mutations (missense, frameshift, and nonsense) in the Forkhead family gene FOXC2 are involved in the distichiasis–lymphedema syndrome. The treatment options are no different for congenital versus acquired distichiasis, with no specific available algorithms. Acquired distichiasis in cicatrizing ocular surface diseases is difficult to manage, and existing treatment options offer success rates of 50%–60%. The outcomes of electroepilation or direct cryotherapy are not as good as surgical excision of distichiatic lashes after splitting the anterior and posterior lamella under direct visualization. The marginal tarsectomy with or without free tarsoconjunctival graft has shown good results in eyes with congenital and acquired distichiasis. The details of differences between normal and distichiatic lash, depth, or course of distichiatic eyelashes remain largely unknown. Studies exploring the distichiatic eyelash depth might improve the outcomes of blind procedures such as cryotherapy or radiofrequency-assisted epilation.     

Potential pitfalls of magnetic resonance imaging in the diagnosis of avascular necrosis

Magnetic resonance (MR) imaging and radionuclide (RN) bone scans were performed in two patients with collagen vascular disease (CVD) to evaluate hip pains. In both patients RN bone scans demonstrated decreased radioactivity in the femoral heads, whereas, MR imaging was normal. Because early changes of avascular necrosis (AVN) frequently present as decreased radioactivity in the femoral head, special attempts were made to detect this decreased activity using pinhole collimator imaging. The diagnosis of AVN was confirmed surgically by venous pressure measurements. Abnormal RN bone scans representing decreased flow due to vasculitis in patients with CVD, may be more sensitive in the diagnosis of AVN before structural changes can be detected on MR studies.