Antihyperglycemic activity of new 1,2,4-oxadiazolidine-3,5-diones.

A series of 1,2,4-oxadiazolidine-3,5-diones was synthesized and evaluated as oral antihyperglycemic agents in the obese insulin resistant db/db and ob/ob mouse - the two models for Type 2 diabetes mellitus. The majority of the prepared methoxy- and ethoxy-linked oxazole 1,2,4-oxadiazolidine-3,5-diones normalized plasma glucose levels at the 100 mg kg(-1) oral dose in the db/db diabetic mouse model, and several amongst them reduced the glucose levels at the 20 mg kg(-1) oral dose. The most potent compounds in the db/db mouse model were also active in the ob/ob mouse model normalizing the plasma glucose levels at the 20 mg kg(-1) oral dose. The trifluoromethoxy analog 32 was the most active compound of the series, reducing significantly the plasma glucose levels at the 5 mg kg(-1) oral dose. Oxadiazole-tailed 1,2,4-oxadiazolidine-3,5-diones were also active in both the db/db and ob/ob diabetic mouse models normalizing plasma glucose levels at the 100 mg kg(-1) oral dose.

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.

Does estradiol mediate leptin's effects on adiposity and body weight?

The role of estradiol in mediating leptin's effects on body weight was assessed in ovariectomized (OVX) mice before and after the onset of obesity. Ovariectomy did not alter leptin levels before the onset of obesity, and estradiol adminstration (0.05-17 microgram/day for 14 days) did not significantly alter leptin levels if they were corrected for the estradiol-induced reduction in body fat. The converse was also true, in that leptin administration (0.4-140 microgram/day) did not alter estradiol levels in intact mice. Furthermore, neither estradiol reduction (via ovariectomy) nor addition (via exogenous administration) significantly altered leptin's ability to reduce fat mass. Leptin was equally effective in reducing body weight in lean or obese OVX mice and intact controls. Finally, estradiol did not change the magnitude of leptin's effect on fat mass reduction when it was given in combination with leptin to lean intact or OVX mice. Estradiol may have indirectly affected leptin efficacy, because leptin did not produce as large a change in fat mass at lower doses in lean OVX mice as it did in intact counterparts. Taken together, these data suggested that 1) estradiol does not directly regulate leptin secretion or its effects on fat mass and 2) leptin does not directly regulate estradiol secretion or its effects on fat mass. Leptin and estradiol, however, may interact in an indirect fashion to affect fat utilization.

Efficacy of exogenous recombinant murine leptin in lean and obese 10- to 12-mo-old female CD-1 mice.

Leptin efficacy was compared in obese and lean female CD-1 mice. Body weights in these 10- to 12-mo-old mice ranged from 29.7 to 62.0 g, and leptin levels correlated with body weight. Mice from the lean and obese ends of the weight distribution were treated with daily peripheral leptin injections (1-100 mg/kg) for a 33-day period. The half-maximal effective doses for weight loss and fat reduction were shifted 0.5-0.7 log to the right for obese mice. Leptin was less efficacious at low doses (1-3 mg/kg) in obese mice but equal to or more efficacious in obese than lean mice at high doses (30-100 mg/kg). Leptin's initial effects on weight loss could be explained by appetite suppression in both groups, but its effects on fat reduction were greater in leptin-treated than pair-fed mice, particularly in the lean group. Leptin also prevented the elevations in serum corticosterone and ketones found in pair-fed lean mice. These data allow a quantitative comparison of leptin sensitivity in obese vs. lean CD-1 mice and suggest that in mice where obesity is a function of outbreeding and age, leptin sensitivity is moderately reduced. Furthermore, although appetite suppression has a clear role in leptin's effects on body weight, leptin may also have specific effects on lipid metabolism and mobilization that are different from the metabolic compensations that normally occur with food deprivation.

Novel 5-(3-aryl-2-propynyl)-5-(arylsulfonyl)thiazolidine-2,4-diones as antihyperglycemic agents.

Novel 5-(3-aryl-2-propynyl)-5-(arylsulfonyl)thiazolidine-2,4-diones and 5-(3-aryl-2-propynyl)-5-(arylsulfanyl)thiazolidine-2,4-diones were prepared and evaluated as oral antihyperglycemic agents in the obese, insulin resistant db/db mouse model at 100 mg/kg and, if the analogue had sufficient potency, 20 mg/kg. The sulfonylthiazolidinediones, 2, were more potent than the corresponding sulfanylthiazolidinedione congeners, 1. With regard to substituent effects on the 3-propynyl phenyl ring (Ar') of 2, 4-halogen substitution generally resulted in the more potent analogues. Substituent effects on the phenylsulfonyl moiety (Ar) of 2 were less clear, although para-halogen substitution on Ar generally was preferable. 2-Pyridinesulfonyl derivatives (Ar = 2-pyridine in 2) also had good potency. Several compounds from series 2 were effective at lowering glucose and insulin in the obese, insulin resistant ob/ob mouse at the 50 mg/kg oral dose. Compound 20 significantly improved the glucose tolerance of obese, insulin resistant Zucker rats at the 20 mg/kg dose level and had no effect on plasma glucose or on glucose tolerance in normal rats fasted for 18 h at the 100 mg/kg level.

Inhibition of glycogenolysis enhances gluconeogenic precursor uptake by the liver of conscious dogs.

We investigated the effect of inhibiting glycogenolysis on gluconeogenesis in 18-h-fasted conscious dogs with the use of intragastric administration of BAY R 3401, a glycogen phosphorylase inhibitor. Isotopic ([3-3H]glucose and [U-14C]alanine) and arteriovenous difference methods were used to assess glucose metabolism. Each study consisted of a 100-min equilibration, a 40-min control, and two 90-min test periods. Endogenous insulin and glucagon secretions were inhibited with somatostatin (0.8 microgram.kg-1.min-1), and the two hormones were replaced intraportally (insulin: 0.25 mU.kg-1.min-1; glucagon: 0.6 ng.kg-1.min-1). Drug (10 mg/kg) or placebo was given after the control period. Insulin and glucagon were kept at basal levels in the first test period, after which glucagon infusion was increased to 2.4 ng.kg-1.min-1; BAY R 3401 decreased tracer-determined endogenous glucose production [rate of glucose production (Ra): 14 +/- 1 to 7 +/- 1 mumol.kg-1.min-1] and net hepatic glucose output (11 +/- 1 to 3 +/- 2 mumol.kg-1.min-1) during test 1. It increased the net hepatic uptake of gluconeogenic substrates from 9.0 +/- 2.0 to 11.6 +/- 0.6 mumol.kg-1.min-1. Basal glycogenolysis was decreased by drug (9.1 +/- 0.7 to 1.5 +/- 0.2 mumol glucosyl U.kg-1.min-1). Placebo had no effect on Ra or the uptake of gluconeogenic precursors by the liver. The rise in glucagon increased Ra by 22 +/- 3 and by 8 +/- 2 mumol.kg-1.min-1 (at 10 min) in placebo and drug, respectively. The rise in glucagon caused little change in the net hepatic uptake (mumol.kg-1.min-1) of gluconeogenic substrates in placebo (8.2 +/- 0.6 to 9.0 +/- 1.0) but increased it markedly (11.6 +/- 0.6 to 15.4 +/- 1.0) in drug. Glucagon increased glycogenolysis by 22.1 +/- 2.5 and by 7.8 +/- 1.6 mumol.kg-1.min-1 in placebo and drug, respectively. The amount of glycogen (mumol glucosyl U/kg) synthesized from gluconeogenic carbon was four times higher in drug (48.6 +/- 9.7) than in placebo (11.3 +/- 1.7). We conclude that BAY R 3401 caused a marked reduction in basal and glucagon-stimulated glycogenolysis. As a result of these changes, there was an increase in the net hepatic uptake of gluconeogenic precursors and in glycogen synthesis.

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.

Overexpression of Glut4 protein in muscle increases basal and insulin-stimulated whole body glucose disposal in conscious mice.

The effect of increased Glut4 protein expression in muscle and fat on the whole body glucose metabolism has been evaluated by the euglycemic hyperinsulinemic clamp technique in conscious mice. Fed and fasting plasma glucose concentrations were 172 +/- 7 and 78 +/- 7 mg/dl, respectively, in transgenic mice, and were significantly lower than that of nontransgenic littermates (208 +/- 5 mg/dl in fed; 102 +/- 5 mg/dl in fasting state). Plasma lactate concentrations were higher in transgenic mice, (6.5 +/- 0.7 mM in the fed and 5.8 +/- 1.0 mM in fasting state) compared with that of non-transgenic littermates (4.7 +/- 0.3 mM in the fed and 4.2 +/- 0.5 mM in fasting state). In the fed state, the rate of whole body glucose disposal was 70% higher in transgenic mice in the basal state, 81 and 54% higher during submaximal and maximal insulin stimulation. In the fasting state, insulin-stimulated whole body glucose disposal was also higher in the transgenic mice. Hepatic glucose production after an overnight fast was 24.8 +/- 0.7 mg/kg per min in transgenic mice, and 25.4 +/- 2.7 mg/kg per min in nontransgenic mice. Our data demonstrate that overexpression of Glut4 protein in muscle increases basal as well as insulin-stimulated whole body glucose disposal. These results suggest that skeletal muscle glucose transport is rate-limiting for whole body glucose disposal and that the Glut4 protein is a potential target for pharmacological or genetic manipulation for treatment of patients with non-insulin-dependent diabetes mellitus.

Regulation of rat glucagon receptor expression.

This report describes the isolation of a cDNA for the rat glucagon receptor by using the glucagon-like peptide 1 receptor cDNA as a probe. Northern blot analysis using the cDNA clone showed that the message encoding the receptor is approximately 2.3 kb in size and is expressed only in liver and kidney among seven tissues tested. To study how glucagon receptor expression is regulated in vivo, the levels of hepatic glucagon receptor mRNA were measured in diabetic mouse model, db/db and control (db/+) mice. Interestingly, the receptor mRNA levels were similar between diabetic and control mice. In contrast, the number of hepatic glucagon receptors in diabetic mice measured by binding assays was significantly higher than that found in normal mice. These results suggest that the major regulation in hepatic glucagon receptor expression in vivo is at the posttranscriptional level.

Novel spirosuccinimides with incorporated isoindolone and benzisothiazole 1,1-dioxide moieties as aldose reductase inhibitors and antihyperglycemic agents.

Compounds from two novel series of spirosuccinimides were prepared. Analogs of series 2 possessed a spiro-fused isoindolone moiety while those of series 3 contained a spiro-fused benzisothiazole S,S-dioxide group. These compounds were evaluated as aldose reductase inhibitors (ARI) in vitro by their ability to inhibit glyceraldehyde reduction using a partially purified bovine lens aldose reductase preparation and in vivo as inhibitors of galactitol accumulation in the lens, sciatic nerve, and diaphragm of galactose-fed rats. Many members from the isoindolone series 2, particularly those containing an isoindolone N-methyl moiety, showed good in vitro and in vivo potency. The most potent member, the 6-chloro analog 32, was resolved, and aldose reductase activity was found to reside almost exclusively in the (+)-enantiomer. Compound 32 was approximately equipotent in the sciatic nerve of the galactose-fed rat to other cyclic imide ARI's of similar in vitro activity, namely sorbinil and ADN-138 and also to tolrestat, an acetic acid-based ARI (ED50's 4-8 mg/kg). Compounds from both series, 2 and 3, were also found to lower plasma glucose levels of genetically obese db/db and ob/ob mice with potency similar to that of ciglitazone. However, members from these series failed to lower insulin levels of the ob/ob mouse at the doses tested.

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.