Behavioral characterization of neuropeptide Y knockout mice.

An extensive behavioral characterization was conducted with mice lacking the gene for neuropeptide Y (NPY) including response to 24 and 48 h fast and challenge with small molecule antagonists of NPY receptors implicated in mediating the feeding effects of NPY (i.e., Y1 and Y5). In addition, wildtype (WT) and NPY knockout (KO) mice were tested in locomotor monitors, elevated plus maze, inhibitory avoidance, acoustic startle, prepulse inhibition, and hot plate assays. One of the major findings was that the NPY KO mice have a reduced food intake relative to WT controls in response to fasting. Also, based on data from the behavioral models, the NPY KO mice may have an anxiogenic-like phenotype, and appear to be hypoalgesic in the hot plate paradigm. The data from these studies provide further evidence of involvement of NPY in energy balance, anxiety, and possibly nociception.

Molecular characterization of a second mouse pancreatic polypeptide receptor and its inactivated human homologue.

The family of mammalian neuropeptide Y (NPY)/peptide YY (PYY)/pancreatic polypeptide (PP) receptors comprises several G protein-coupled receptors, i.e. Y1, Y2, and Y4/PP1. We now report cloning of a novel member of this family named PP2. The coding region of the mouse PP2 gene reveals no introns and predicts a seven transmembrane domain (TM) receptor of 371 amino acids. Percent identities of the mouse PP2 to mouse Y1, mouse Y4/PP1 and human Y2 receptors are 53, 42, and 31, respectively. The mouse PP2 receptor expressed in COS cells binds rat 125I-PP with high affinity, i.e. IC50 = 65 pM. Pharmacological characterization of 125I-PP binding shows a rank order of potency of PP >> PYY >/= NPY, which is similar to that of the mouse Y4/PP1 receptor. Mouse PP2 transcripts were not detectable by Northern analysis in adult tissues and in 11-, 15-, and 17-day-old embryos. However, a 9.8-kb PP2 transcript was detectable in 7-day-old mouse embryo, i.e. prior to the organogenesis of pancreas and the onset of PP production. We have also cloned the human homologue of PP2, which is a single copy gene and maps to human chromosome 5q31. Surprisingly, the human PP2 cDNAs and gene sequences display a single base deletion in the coding region. This frameshifting mutation predicts a truncated receptor of 290 amino acids without TM7. Transfection of COS-7 cells with several different human PP2 expression constructs failed to confirm any specific binding of 125I-PP, 125I-PYY, or 125I-NPY to cell membranes. These data suggest that in mouse there are at least two PP receptors, Y4/PP1 and PP2, whereas in humans, PP2 is either functionally inactive or it has acquired a PP-independent function.

Identification of a novel hypothalamic neuropeptide Y receptor associated with feeding behavior.

Neuropeptide Y (NPY) plays important roles in the central control of appetite and energy balance, but the receptor subtype responsible for this function has not been cloned. Here we report the cloning by expression of a novel NPY receptor subtype from a rat hypothalamus cDNA library. The novel receptor, referred to as the NPY Y5 receptor, has a transcript of approximately 2.6 kilobases with an open reading frame of 1335 base pairs that encodes a 445-amino acid protein. The amino acid sequence deduced from the rat Y5 cDNA clone shows only 30-33% identity to other NPY receptors, including Y1, Y2, and Y4/PP1. Using the rat Y5 receptor cDNA probe, the human homologue was obtained by low stringency hybridization. The human Y5 amino acid sequence has 88% identity to the rat Y5 receptor. Importantly, pharmacological analysis shows that the rat and human Y5 receptors have high affinity for the peptides that elicit feeding (e.g. NPY, PYY, (2-36)NPY, and (LP)NPY) and low affinity for nonstimulating peptides (e.g. (13-36)NPY and rat PP), suggesting that it is the NPY feeding receptor subtype.

New potent antihyperglycemic agents in db/db mice: synthesis and structure-activity relationship studies of (4-substituted benzyl) (trifluoromethyl)pyrazoles and -pyrazolones.

The synthesis, structure-activity relationship (SAR) studies, and antidiabetic characterization of 1,2-dihydro-4-[[4-(methylthio)phenyl]methyl]-5-(trifluoromethyl)-3H- pyrazol-3-one (as the hydroxy tautomer; WAY-123783, 4) are described. Substitution of 4-methylthio, methylsulfinyl, or ethyl to a benzyl group at C4, in combination with trifluoromethyl at C5 of pyrazol-3-one, generated potent antihyperglycemic agents in obese, diabetic db/db mice (16-30% reduction in plasma glucose at 2 mg/kg). The antihyperglycemic effect was associated with a robust glucosuria (> 8 g/dL) observed in nondiabetic mice. Chemical trapping of four of the seven possible tautomeric forms of the heterocycle by mono- and dialkylation at the acidic hydrogens provided several additional potent analogs (39-43% reduction at 5 mg/kg) of the lead 4 as well as a dialkylated pair of regioisomers that showed separation of the associated glucosuric effect produced by all of the active analogs in normal mice. Further pharmacological characterization of the lead WAY-123783 (ED50 = 9.85 mg/kg, po in db/db mice), in oral and subcutaneous glucose tolerance tests, indicated that unlike the renal and intestinal glucose absorption inhibitor phlorizin, pyrazolone 4 does not effectively block intestinal glucose absorption. SAR and additional pharmacological data reported herein suggest that WAY-123783 represents a new class of potent antihyperglycemic agents which correct hyperglycemia by selective inhibition of renal tubular glucose reabsorption.

Cloning and characterization of a novel receptor to pancreatic polypeptide, a member of the neuropeptide Y receptor family.

We report isolation of a murine gene, NPYR-D, which predicts an intronless novel G protein-coupled receptor of 375 amino acids. Percent identities of NPYR-D to the clone Y1, Y2, rat Y4/PP1 and human Y4/PP1 receptors are 45, 32, 92 and 76, respectively. Southern blots indicate that NPYR-D and human Y4/PP1 receptor genes are species homologues. Rat [125I]pancreatic polypeptide ([125I]rPP) bound to NPYR-D transfected COS-7 cell membranes with a high affinity, i.e. IC50=90 pM. Pharmacological characterization of [125I]rPP binding showed a rank order of potency of P >> PYY > or = NPY, such that PYY and NPY were at least 5000-fold weaker than PP. Interestingly, [125I]rPYY binding produced the same rank order, but PYY and NPY were only 25-fold weaker than PP, which had an IC50 value of approximately 120 pM. Tissue distribution studies in mouse and humans suggest potential roles of this novel receptor in the gastrointestinal tract, heart, prostate, as well as in neural and endocrine signalling.

Studies on new acidic azoles as glucose-lowering agents in obese, diabetic db/db mice.

Bioisosteric substitution was used as a tool to generate several new structural alternatives to the thiazolidine-2,4-dione and tetrazole heterocycles as potential antidiabetic agents. Among the initial leads that emerged from this strategy, a family of acidic azoles, isoxazol-3- and -5-ones and a pyrazol-3-one, showed significant plasma glucose-lowering activity (17-42% reduction) in genetically obese, diabetic db/db mice at a dose of 100 mg/kg/day x4. Structure-activity relationship studies determined that 5-alkyl-4-(arylmethyl)pyrazol-3-ones, which exist in solution as aromatic enol/iminol tautomers, were the most promising new class of potential antidiabetic agent (32-45% reduction at 20 mg/kg/d x4). Included in this work are convenient syntheses for several types of acidic azoles that may find use as new acidic bioisosteres in medicinal chemistry such as the antidiabetic lead 5-(trifluoromethyl)pyrazol-3-one (hydroxy tautomer) and aza homologs of the pyrazolones, 1,2,3-triazol-5-ones (hydroxy tautomer) and 1,2,3,4-tetrazol-5-one heterocycles. log P and pKa data for 15 potential acidic bioisosteres, all appended to a 2-naphthalenylmethyl residue so as to maintain a similar distance between the acidic hydrogen and arene nucleus, are presented. This new data set allows comparison of a wide variety of potential acid mimetics (pKa 3.78-10.66; log P -0.21 to 2.76) for future drug design.

Metabolic abnormalities of the hyperglycemic obese Zucker rat.

In a cross-sectional study, we evaluated the metabolic profiles of lean (Fa/?) and obese (fa/fa) Zucker male rats at 4 to 8 months of age. Although all of the obese rats (N = 108) demonstrated glucose intolerance, most of the obese rats exhibited only mild elevations of fasted and fed plasma glucose. Only 14 of the obese rats were severely hyperglycemic, which resulted in substantial elevations of glycohemoglobin (GHb) levels. The nerve and lens levels of glucose, sorbitol, and fructose were elevated, and the myo-inositol was depleted in all hyperglycemic obese rats, but not in the euglycemic obese rats. With increasing duration of hyperglycemia, the neural myo-inositol level approached normal, while the lenses became cataractous. All obese rats had increased urinary albumin excretion (UAE), which was dependent on age (r = .45, P less than .02) and independent of hyperglycemia, glucosuria, and polyuria. In conclusion, although the euglycemic obese rats exhibited some diabetic abnormalities, the hyperglycemic obese Zucker rat more closely resembled the altered metabolic profile associated with type II diabetes mellitus.

Antihyperglycemic activity of novel substituted 3H-1,2,3,5-oxathiadiazole 2-oxides.

A series of substituted 3H-1,2,3,5-oxathiadiazole-2-oxides (6) was prepared and tested for antihyperglycemic activity in the db/db mouse, a model for type 2 (non-insulin dependent) diabetes mellitus. The oxathiadiazoles 6 were synthesized by a two-step sequence: treatment of a substituted acetonitrile (4) with hydroxylamine to give the corresponding amidoxime (5) and cyclization with thionyl chloride to yield 6. In terms of potency, the 2-naphthalenylmethyl group (as in compound 3) was found to be the optimal substituent in this series. Compound 3 was approximately 5 times more potent than ciglitazone (1).

Perfluorocarbon-based antidiabetic agents.

In a preliminary communication (J. Med. Chem. 1989, 32, 11-13) a series of perfluoro-N-[4-(1H-tetrazol-5ylmethyl)phenyl]alkana mides (perfluoro anilides I), designed as novel analogues of ciglitazone, were reported to possess oral antidiabetic activity in two genetic animal models of non-insulin-dependent diabetes mellitus (NIDDM): obese (ob/ob) and diabetic (db/db) mice. In this report, the results from a structure-activity relationship (SAR) study of the series I are described. Comprehensive statistical analysis among the 86 analogues screened for blood glucose lowering in ob/ob mice was achieved by a new application of a general statistical procedure which made it possible to make meaningful comparisons between more than 140 separate experiments (N = 2966). Perfluoro anilides I lowered plasma glucose in the hyperglycemic ob/ob and db/db mice but not in euglycemic normal rats. In the hyperinsulinemic ob/ob mouse, decreases in plasma insulin levels paralleled the decline in plasma glucose. Potency and efficacy in the series was shown to be dependent on the length of the perfluorocarbon chain (RF) of I. Optimal activity occurred with the C7 and C8 RF chains. The more extensive SAR studies reported here, indicated that the lipophilic RF chain is the most important structural element of I since neither the phenyl nor tetrazole rings present in anilides I were necessary for antihyperglycemic activity while medium length (C7-C8) RF chains, especially the C7F15 chain, were shown to confer antihyperglycemic activity in ob/ob mice to a wide variety of structures.

Intervention with the aldose reductase inhibitor, tolrestat, in renal and retinal lesions of streptozotocin-diabetic rats.

The progressive increase in urinary albumin excretion, which precedes the development of diabetic nephropathy, can be prevented in diabetic rats if the aldose reductase inhibitor, tolrestat, is administered at the initiation and throughout the duration of hyperglycaemia. We therefore determined the ability of tolrestat to intervene in the further progression of already established urinary albumin excretion of streptozotocin-diabetic female Wistar rats. Two months after streptozotocin injection, diabetic rats were grouped as low-urinary albumin excretion (0.2-1.0 mg albumin/day) or high-urinary albumin excretion (1.9-5.9 mg albumin/day), at which time tolrestat intervention (25 mg/kg per day) was begun for half of the diabetic rats in each urinary albumin excretion group. After six months of treatment tolrestat caused a significant reduction in the urinary albumin excretion rate of the low-urinary albumin excretion group only. The diabetes-induced rise of total urinary protein in both groups was significantly reduced by tolrestat. Furthermore, the diabetes-induced increase (49%) in the thickness of the basement membranes of retinal capillaries from the outer plexiform layer was significantly diminished by tolrestat administration. In conclusion, intervention therapy with the aldose reductase inhibitor, tolrestat, can reduce the progression of urinary albumin excretion and retinal basement membrane thickening in long-term diabetic rats.

Degenerated intramural pericytes ('ghost cells') in the retinal capillaries of diabetic rats.

One of the earliest histopathological signs of diabetic retinopathy is a selective loss of intramural pericytes from retinal capillaries. In the present study, the retinal vessels of rats with streptozotocin-induced diabetes (STZ Wistar) and rats with genetically-induced insulin dependent diabetes mellitus (BB Wistar) and non-insulin dependent diabetes mellitus (SHR/N-corpulent) were examined after 6 to 8 months duration for diabetes-related retinal microangiopathies. The SHR/N-corpulent (cp) rats were fed a 54% sucrose diet, whereas the STZ Wistar and BB Wistar rats were fed laboratory chow for 32 to 36 weeks. In all the diabetic rats, the retinal capillaries in enzyme-digested flat mounts exhibited an increase in periodic-acid-Schiff (PAS) staining and loss of pericytes compared to their respective euglycemic controls. Pericyte "ghosts", like those defined in human diabetes as intramural pockets lacking normal cell contents, were documented by high resolution micrographs in all the diabetic rats. Endothelial cell proliferation, capillary dilation, and varicose loop formation were noted in some of the diabetic rats. Hence, similar capillary lesions were found in very different groups of diabetic rats. The findings suggest that a chronic high tissue concentration of glucose is the underlying factor which triggers pathogenesis in the pericyte. Hyperglycemia-induced activation of endogenous aldose reductase of the polyol pathway is probably the initial insult, but other factors such as advanced glycosylation products may affect the final outcome.

Synthesis and antihyperglycemic activity of novel 5-(naphthalenylsulfonyl)-2,4-thiazolidinediones.

A series of 5-(naphthalenylsulfonyl)-2,4-thiazolidinediones were synthesized and evaluated for antihyperglycemic activity in an insulin-resistant, genetically diabetic db/db mouse model of non-insulin-dependent diabetes mellitus (NIDDM). The sulfones could be synthesized by a novel, selective C-5 sulfonylation of dilithio-2,4-thiazolidinedione with appropriate sulfonyl chlorides. Within this series, naphthalene was found to be superior to other groups for eliciting antihyperglycemic activity, including the p-alkoxyphenyl group found in ciglitazone, a prototypical agent for this activity. Attachment of the 5-sulfonyl-2,4-thiazolidinedione moiety to the 2-naphthalene position led to optimum activity. Other linkers between the naphthalene and 2,4-thiazolidinedione rings, such as thio, methylene, oxy, and sulfinyl led to decreased antihyperglycemic activity. The best analogue, 5-(2-naphthalenylsulfonyl)-2,4-thiazolidinedione (AY-31,637) was equipotent to ciglitazone in two animal models of NIDDM.

Prevention of urinary albumin excretion in 6 month streptozocin-diabetic rats with the aldose reductase inhibitor tolrestat.

Recent clinical data strongly suggest that elevated urinary albumin excretion (UAE) identifies diabetic subjects at risk of developing nephropathy. Elevated UAE is attributed to increased transglomerular pressure, which is associated with poor metabolic control in rats. Because excess glucose in diabetes is metabolized via the polyol pathway, we were interested in whether the diabetes-induced elevation in UAE in rats could be prevented by inhibiting aldose reductase (AR), the first enzyme in the polyol pathway, with the AR inhibitor tolrestat. In fact, in rats made diabetic with streptozocin (35 mg/kg IV), treatment for 6 months with tolrestat (25 mg/kg/day in the diet) prevented both sorbitol accumulation in the kidney and the increase in UAE. Sorbitol accumulation and the increased UAE were not associated with statistically significant mesangial expansion, and the thickening of glomerular basement membranes was not affected by tolrestat treatment. The authors conclude that the 4.7-fold elevation in UAE in chronically diabetic rats is linked to the increased flux of glucose through the polyol pathway since it was prevented by inhibiting aldose reductase with tolrestat.

Characterization and partial purification of a factor from uremic human serum that induces insulin resistance.

We have previously shown that the incubation of normal rat adipose tissue with sera from nondialyzed, nondiabetic uremic patients reduces the transport and metabolism of glucose, in the absence and presence of insulin. In this study insulin-stimulated glucose metabolism by normal rat adipocytes was used as a bioassay to identify the resistance activity, assess the effect of chemical modification on it, and the clinical states associated with its production. The resistance activity was trypsin-labile and had an apparent isoelectric point between 6 and 7, but was not retained by either protein A or concanavalin A columns. The insulin resistance activity was decreased by coincubation with the protein synthesis inhibitor, cycloheximide. Purification to greater than 200,000-fold was attained by heating (100 degrees C) uremic serum, subjecting the supernatant to Sephadex G-25 chromatography and subsequent adsorption to DEAE at pH 7.8 and elution at pH 6.5. The partially purified resistance activity was retained within dialysis tubing of 1,000-mol wt cutoff but not within 2,000-mol wt cutoff. Hemodialysis of patients over 1 wk to 18 mo reduced significantly the amount of resistance activity in their sera. The resistance activity, present in most uremic patients, was not found in the sera of individuals with normal renal function but who were either obese, fasted, elderly or had type II diabetes mellitus. Thus, a circulating small molecular weight peptide, unique to uremia, induced insulin resistance by a protein synthesis-dependent mechanism.

Sulfonylurea effects on target tissues for insulin.

We have examined the nonpancreatic actions of sulfonylureas on multiple aspects of insulin responsiveness in two target tissues for insulin, liver and fat. In vivo administration of tolazamide and glipizide reduced significantly the postabsorptive serum glucose levels in rats without altering the levels of insulin. This was consistent with extrapancreatic sites of drug action. The number and affinity of hepatic insulin receptors was not different from those of control rats. Using a tissue culture system for rat adipose tissue, a 20-h treatment with sulfonylureas markedly potentiated insulin action in fat cells. The primary augmentation was at the level of insulin-stimulated glucose transport. Again, there was no alteration of the insulin receptors located on the adipose tissue. Furthermore, consistent with the lack of an influence on insulin-induced receptor loss after in vitro treatment with sulfonylureas, the in vivo administration of these agents did not alter the transglutaminase activity in rat hepatic tissue. The data demonstrate that sulfonylureas potentiate the responsiveness of the target tissues for insulin. Thus, these hypoglycemic agents probably act by correcting some of the cellular lesions associated with the insulin resistance in type II diabetes mellitus.

Induction of insulin resistance in normal adipose tissue by uremic human serum.

An incubation of uremic human serum with normal rat adipose tissue will make the subsequently isolated adipocytes less responsive to insulin. To examine the extent of insulin resistance, we obtained sera from nondiabetic, uremic patients, who had not undergone dialysis therapy. The sera were then dialyzed (3500 molecular-weight cutoff) for 18 hr against a defined culture medium to eliminate possible in vitro effects of altered levels of end-product metabolites, electrolytes, and metabolic substrates. After an incubation of epididymal fat tissue from normal rats, for 3 hr with the dialyzed sera (50% vol/vol), cells were isolated and washed. The insulin stimulation of 14C-glucose (0.2 mM) incorporation to 14CO2 and total lipids was significantly reduced in the adipocytes pretreated with sera from 19 of the 29 uremic patients. Although elevated in the uremic patients, the sera levels of insulin, and parathyroid and growth hormones were not correlated to insulin resistant activity. Furthermore, incubation of adipose tissue for 3 hr with insulin, glucagon, or PTH did not produce resistance. The uremic sera reduced glucose utilization equally at 0.2 and 50 mM glucose, suggesting that the insulin resistance was induced additionally at a site distal to the glucose transport system. However, the concentration of insulin (22 microunits/ml) required for half-maximal stimulation of glucose metabolism was not altered by pretreatment with uremic serum. Also, neither the isoproterenol-stimulated lipolysis nor the inhibition of this cellular event was influenced by pretreatment with uremic sera.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular basis of insulin resistance in chronic uremia.

To define the cellular alterations responsible for insulin resistance during uremia, we studied insulin action in adipocytes isolated from rats 2 wk after 75% partial nephrectomy. Insulin binding to fat cells and purified liver plasma membranes prepared from uremic rats was unaltered. In contrast, hexose transport was significantly decreased, with and without insulin, in the fat cells from the uremic animals. The concentration of insulin that elicited half-maximal response was not altered. Glucose utilization was reduced in the absence or presence of insulin by partial nephrectomy. The stimulation of hexose transport and glucose metabolism by the insulin mimickers, hydrogen peroxide and vitamin K5, were also inhibited. Hexose transport activity in adipocytes obtained from uremic rats was no longer decreased when pieces of fat tissue were cultured for 20 h. Finally, hexose transport was reduced in the cells isolated from normal adipose tissue that was preincubated for 3 h with uremic serum, but insulin binding was not different than control. Thus, insulin resistance associated with uremia may be primarily accounted for by altered postreceptor events that appear to result from a circulating factor(s).

Extrapancreatic action of sulfonylureas: hypoglycemic effects are not dependent on altered insulin binding or inhibition of transglutaminase.

It has been proposed by others that sulfonylureas exert their extrapancreatic hypoglycemic effects by increasing insulin binding through inhibition of receptor-mediated hormone internalization. In this study, we examined the possibility that the drugs act by inhibiting transglutaminase, an enzyme thought important in the internalization process. For ten days, male rats were fed pulverized chow containing either no drug, glipizide (5 mg/kg initial body wt/d), or tolazamide (75 mg/kg initial body wt/d). Prior to sacrifice, the six-hour fasting level of serum glucose was significantly reduced from 96 mg/100 ml in the control rats to 81 and 42 mg/100 ml in the glipizide- and tolazamide-treated rats, respectively. In contrast, the serum level of insulin was similar for all groups. The activity of transglutaminase in the postnuclear fraction of liver homogenate also was the same for all experimental groups. The specific binding of labeled insulin to purified liver plasma membranes was examined over a broad range of insulin concentrations; once again, there was no difference between experimental groups. Thus, the hypoglycemia caused by sulfonylurea administration could not be attributed to increases in insulin binding, inhibition of transglutaminase activity, or enhanced insulin levels. These data support our previous suggestion, based on in vitro studies, that sulfonylureas act predominately on processes beyond the binding portion of the insulin receptor.