Flavones Inhibit the Activity of AKR1B10, a Promising Therapeutic Target for Cancer Treatment

AKR1B10 is an NADPH-dependent reductase that plays an important function in several physiological reactions such as the conversion of retinal to retinol, reduction of isoprenyl aldehydes, and biotransformation of procarcinogens and drugs. A growing body of evidence points to the important role of the enzyme in the development of several types of cancer (e.g., breast, hepatocellular), in which it is highly overexpressed. AKR1B10 is regarded as a therapeutic target for the treatment of these diseases, and potent and specific inhibitors may be promising therapeutic agents. Several inhibitors of AKR1B10 have been described, but the area of natural plant products has been investigated sparingly. In the present study almost 40 diverse phenolic compounds and alkaloids were examined for their ability to inhibit the recombinant AKR1B10 enzyme. The most potent inhibitors-apigenin, luteolin, and 7-hydroxyflavone-were further characterized in terms of IC50, selectivity, and mode of action. Molecular docking studies were also conducted, which identified putative binding residues important for the interaction. In addition, cellular studies demonstrated a significant inhibition of the AKR1B10-mediated reduction of daunorubicin in intact cells by these inhibitors without a considerable cytotoxic effect. Although these compounds are moderately potent and selective inhibitors of AKR1B10, they constitute a new structural type of AKR1B10 inhibitor and may serve as a template for the development of better inhibitors.

Pharmacokinetic interactions of breast cancer chemotherapeutics with human doxorubicin reductases

Paclitaxel (PTX), docetaxel (DTX), 5-fluorouracil (5-FU), cyclophosphamide (CYC) or tamoxifen (TMX) are combined with doxorubicin (DOX) in first-line chemotherapy regimens that are indicated for breast cancer patients. Although the efficacies of these drugs in combination treatments have been demonstrated in clinical practice, their possible interference with DOX metabolism has not been described in detail to date. In the present study, we investigated the possible interactions of human carbonyl reducing enzymes with 5-FU, PTX, DTX, CYC and TMX. First, the reducing activities of carbonyl reducing enzymes toward DOX were tested using incubations with purified recombinant enzymes. In the subsequent studies, we investigated the possible effects of the tested anticancer agents on the DOX-reducing activities of the most potent enzymes (AKR1C3, CBR1 and AKR1A1) and on the DOX metabolism driven by MCF7, HepG2 and human liver cytosols. In both of these assays, we observed that CYC and its active metabolites inhibited DOX metabolism. In the final study, we tracked the changes in AKR1C3, CBR1 and AKR1A1 expression levels following exposure to the tested cytostatics in MCF7 and HepG2 cells. Consequently, no significant changes in the expression levels of tested enzymes were detected in either cell line. Based on these findings, it is feasible to presume that inhibition rather than induction plays a role in the interactions of the tested anticancer agents with DOX-reducing enzymes. In conclusion, our results describe important molecular events that occur during combination breast cancer therapies and might modulate pharmacokinetic DOX resistance and/or behaviour.

Isoquinoline alkaloids as a novel type of AKR1C3 inhibitors

AKR1C3 is an important human enzyme that participates in the reduction of steroids and prostaglandins, which leads to proliferative signalling. In addition, this enzyme also participates in the biotransformation of xenobiotics, such as drugs and procarcinogens. AKR1C3 is involved in the development of both hormone-dependent and hormone-independent cancers and was recently demonstrated to confer cell resistance to anthracyclines. Because AKR1C3 is frequently upregulated in various cancers, this enzyme has been suggested as a therapeutic target for the treatment of these pathological conditions. In this study, nineteen isoquinoline alkaloids were examined for their ability to inhibit a recombinant AKR1C3 enzyme. As a result, stylopine was demonstrated to be the most potent inhibitor among the tested compounds and exhibited moderate selectivity towards AKR1C3. In the follow-up cellular studies, stylopine significantly inhibited the AKR1C3-mediated reduction of daunorubicin in intact cells without considerable cytotoxic effects. This inhibitor could therefore be used as a model AKR1C3 inhibitor in research or evaluated as a possible therapeutic anticancer drug. Furthermore, based on our results, stylopine can serve as a model compound for the design and future development of structurally related AKR1C3 inhibitors.

Diagnosis and treatment of diabetic ketoacidosis and the hyperglycemic hyperosmolar state

Diabetic ketoacidosis and the hyperglycemic hyperosmolar state are the most serious complications of diabetic decompensation and remain associated with excess mortality. Insulin deficiency is the main underlying abnormality. Associated with elevated levels of counterregulatory hormones, insulin deficiency can trigger hepatic glucose production and reduced glucose uptake, resulting in hyperglycemia, and can also stimulate lipolysis and ketogenesis, resulting in ketoacidosis. Both hyperglycemia and hyperketonemia will induce osmotic diuresis, which leads to dehydration. Clinical diagnosis is based on the finding of dehydration along with high capillary glucose levels with or without ketones in the urine or plasma. The diagnosis is confirmed by the blood pH, serum bicarbonate level and serum osmolality. Treatment consists of adequate correction of the dehydration, hyperglycemia, ketoacidosis and electrolyte deficits.

Long-term use of intramuscular insulin therapy in a type I diabetic patient with subcutaneous insulin resistance

We studied a 26-year-old Type 1 diabetic patient who experienced recurrent episodes of ketoacidosis and who was unresponsive to subcutaneous insulin, but normally responsive to intravenous insulin as demonstrated by insulin challenge test. Attempts at intravenous and intraperitoneal insulin administration were complicated by recurrent septicaemia. We therefore investigated the hypoglycaemic effect of intramuscular insulin administration in this patient. After intramuscular injection of NPH and Ultralente human insulin (0.1 U kg-1), the lowest plasma glucose levels occurred 1 and 7 h later, respectively; the hypoglycaemic effect lasted approximately 2 and 12 h, respectively. We based insulin therapy on intramuscular NPH as a fast-acting insulin and Ultralente as an intermediate-acting insulin using four injections a day. During the next 24 months, the patient was hospitalized for 4 weeks versus 56 weeks in the 20 months preceding intramuscular insulin administration, and was able to resume full-time work. HbAlC decreased from 11.7% to 8.7% (normal range: 4.2-5.9%). Thus, long-term intramuscular insulin therapy is a feasible alternative to intravenous or intraperitoneal insulin in patients with well-demonstrated resistance to subcutaneous insulin.

Calcium is essential in normalizing intolerance to glucose that accompanies vitamin D depletion in vivo

Vitamin D is essential for normal insulin secretion in vivo and in vitro. The differential effect of calcium and of the vitamin D endocrine system in the insulin response to secretagogues is still a subject of debate. To study the roles of calcium and the vitamin D system in the in vivo insulin response, GTT and insulin sensitivity tests were conducted in rats presenting vitamin D depletion and hypocalcemia or vitamin D depletion supplemented with calcium alone for 3, 7, or 14 days, vitamin D3 (6.5 nmol/day x 7 days), or 1,25(OH)2D3 (28 pmol/day x 7 days). Serum calcium was 1.28 +/- 0.04 mM in hypocalcemic vitamin D-depleted rats, 1.47 +/- 0.06 (NS), 1.8 +/- 0.2 (P < 0.0002), and 2.04 +/- 0.07 (P < 0.0001) mM after 3, 7, or 14 days, respectively, of calcium supplementation; vitamin D3- or 1,25(OH)2D3-supplemented animals had serum calcium of 2.61 +/- 0.04 or 2.48 +/- 0.05 mM (P < 0.0001 vs. hypocalcemic vitamin D-depleted rats). Rats with hypocalcemia and vitamin D depletion had significantly higher glucose concentrations (P < 0.0005) and lower insulin response during GTT than all other groups (P < 0.001). Differences in insulin sensitivity could not account for differences in response because exogenous insulin administration led to a similar drop in glucose concentrations in all groups, with the nadir averaging 51.7 +/- 2.6% of initial values. To distinguish between calcium and the vitamin D system in the GTT response, rats were treated with a nonhypercalcemic analogue of 1,25(OH)2D3, OCT (28 pmol/day x 4-7 days) with or without dietary calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin D depletion retards the normal regeneration process after partial hepatectomy in the rat

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], the hormone of the vitamin D3 (D3) endocrine system, has been shown to influence malignant and normal cell proliferation/differentiation, while insulin (I) is known to be essential for liver growth. To investigate the influence of D3 on liver regeneration, the effect of the D status was studied in D-depleted rats (D-) pretreated with: G1, placebo (D-, hypocalcemic); G2, oral calcium only (D-, normocalcemic); G3, D3; and G4, 1,25-(OH)2D3. Two thirds hepatectomy (HX) or sham operation was performed, and regeneration was studied for 3 weeks. I response to glucose challenge and the hepatic I receptor were also studied. Cell volume, DNA, and RNA were not affected by pretreatment. After HX, the pattern of [3H]thymidine incorporation into DNA (P less than 0.003) and the cell labeling index (P less than 0.0001) were highly influenced by pretreatment and suggestive of an earlier appearance of the S phase of the cell cycle in the 1,25-(OH)2D3-treated compared to the D- hypocalcemic group. Furthermore, the mitotic index revealed a significant effect of pretreatment (P less than 0.01), with peak mitosis 24 h after HX in D3-treated and 1,25-(OH)2D3-treated rats compared to 30-36 h after HX in the D- groups. Liver weight restitution was impaired in D- rats (P less than 0.009) and is illustrated by the estimated time required to achieve 70% recovery of the resected liver mass, which was found to be 186 and 300 h in G1 and G2, and 154 and 107 h in G3 and G4. G1 rats had significantly higher glucose concentrations (fasting as well as after glucose injection) and reduced I secretion when challenged with glucose (P less than 0.001); they also had an upregulation in hepatic I receptor number (P less than 0.005) compared to calcium or D3-treated rats, while 1,25-(OH)2D3 led to a liver I receptor number similar to that found in hypocalcemic D- rats; the affinity of the I receptor was, however, only slightly changed by pretreatment (P less than 0.08). Our data indicate that in D depletion, hypocalcemia retards DNA synthesis and liver mass recovery, while normocalcemia contributes to DNA synthesis, but fails to sustain mitosis and compensatory liver growth to a level comparable to that found after D3 and/or 1,25-(OH)2D3 repletion. The observation that both D3 and 1,25-(OH)2D3 significantly promoted normal liver recovery after partial HX illustrates the role of the D endocrine system in normal cell physiology in vivo.

Blood glucose measurements during symptomatic episodes in patients with suspected postprandial hypoglycemia

Postprandial (reactive) hypoglycemia is a controversial disorder because its symptoms are not specific, the presence of symptoms often correlates weakly with blood glucose concentrations measured after oral glucose administration, and glucose levels have rarely been measured when symptoms have developed spontaneously. In this study, we measured blood glucose in 28 patients with suspected postprandial hypoglycemia while they were experiencing their typical symptoms, in capillary blood collected on filter paper. Five patients (18 percent) had symptoms of "hypoglycemia" that were associated with blood glucose levels of 2.8 mmol per liter (50 mg per deciliter) or less, and eight other patients (29 percent) had symptoms associated with glucose levels of 2.9 to 3.3 mmol per liter on at least one occasion. Six (5 percent) of 132 reported symptomatic episodes that were associated with blood glucose levels of 2.8 mmol per liter or less, and 16 (12 percent) with levels of 2.9 to 3.3 mmol per liter. In 140 measurements made in 17 normal subjects, blood glucose levels were never found to be less than 2.8 mmol per liter, and levels of 2.9 to 3.3 mmol per liter were found only twice. No specific symptom was associated with low glucose levels in the patients with suspected hypoglycemia. The relief of symptoms by ingesting food was more often associated with low than with normal blood glucose levels: 86 percent of episodes in which blood glucose values were less than or equal to 3.3 mmol per liter were relieved by eating, as compared with 53 percent of episodes in which values were more than 3.3 mmol per liter (P less than 0.007). No correlation was found between plasma glucose levels measured after oral glucose administration and blood glucose levels measured during symptoms. We conclude that postprandial hypoglycemia is infrequent, even in a referral population, and that recording blood glucose measurements during spontaneously occurring symptomatic episodes is necessary to establish the diagnosis since symptoms are not specific and oral glucose-tolerance testing is not helpful.

Suppression of T4 secretion in a metastatic follicular carcinoma

Despite total thyroidectomy, a patient with metastatic follicular carcinoma of the thyroid remained biologically euthyroid three months after stopping thyroxine (T4) therapy. Thyroid hormone production was investigated by means of a modified tri-iodothyronine (T3) suppression test, in which serum T4 was used as a suppression marker. After three weeks of oral T3 (Cytomel) therapy (50 micrograms/day), the serum T4 decreased from normal (108 nmol/L) to undetectable values. However, even though suppressive therapy was effective in preventing TSH dependent hormone secretion by the tumor, it did not prevent tumor growth and the eventual death of the patient.

Effects of continuous subcutaneous insulin infusion versus multiple injections on insulin receptors in insulin-dependent diabetics

We compared continuous subcutaneous insulin infusion (CSII) versus multiple injections (MI) in the treatment of insulin-dependent diabetes mellitus (IDDM) to assess the effect of glucose control on monocyte insulin receptors. Each IDDM patient (n = 8) was treated for 2 mo by MI (HS Ultralente and AC boluses of regular insulin) and for 2 mo by CSII in a randomized fashion. Prestudy preprandial/postprandial blood glucose levels were 199 +/- 33/261 +/- 28 mg/dl and improved to 124 +/- 12/156 +/- 13 mg/dl during MI and to 115 +/- 11/151 +/- 11 mg/dl during CSII. Glycosylated hemoglobin before the study was 10.1 +/- 0.5% and decreased to 8.8 +/- 0.4 and 8.3 +/- 0.3% during MI and CSII, respectively. The specific 125I-labeled insulin binding to circulating monocytes in a group of nonobese controls (n = 17) was 4.6 +/- 0.2%. In our poorly controlled diabetics during conventional therapy, the 125I-insulin binding was decreased to 3.7 +/- 0.3 (P less than .025). This was not significantly affected by MI despite good glucose control (4.0 +/- 0.3%). With CSII, however, good glucose control was associated with normalization of 125I-insulin binding to monocytes (4.7 +/- 0.27%). The affinity of the insulin receptors was normal before the study and was not affected by either MI or CSII. In conclusion, these observations demonstrate that in IDDM, intensive therapy by MI and CSII resulted in similar good glucose control, but only CSII resulted in normalization of insulin receptors on circulating monocytes.

Characteristics of patients with normal T3 and T4 and a low TSH response to TRH

The nature of the thyroid disorder presented by patients with normal T4 and T3 but blunted TSH response to TRH has not been clarified. In this study, we compared thyroid function tests in 16 such patients with those of 14 controls and 10 hyperthyroid patients. Basal total T4, free T4, total T3, iodine uptake and cholesterol of the study group were similar to controls but significantly (P less than 0.001) lower than in hyperthyroid patients, except for cholesterol which was higher. In contrast, the basal TSH, increase in TSH after TRH stimulation, and decrease of T4 during T3 suppression tests were similar to data obtained in hyperthyroid patients but significantly (P less than 0.001) lower than in controls. Pulse rate was mid-way between the control and the hyperthyroid group. Thyroid stimulating antibody (TSAb) was measured with human thyroid cells in culture; the assay was positive in four subjects in the 16-patient group and in all hyperthyroid patients tested. TSH stimulation test showed a hyporesponse in iodine uptake in the four patients with positive TSAb (26 +/- 29%), as well as in hyperthyroid patients (6 + 5%). However, there was a hyper-response to TSH (213 +/- 52%) in the remaining 12 patients in the group, none of whom had TSAb. Thus TSAb is not seen as responsible for the thyroid disorder in the majority of patients with normal T3 and T4 and absent or blunted TSH response to TRH; surprisingly, most of these patients have thyroid hypersensitivity to TSH. These two characteristics, absence of TSAb and hypersensitivity to TSH, delineate a thyroid disorder clearly different from Graves' disease.

Effect of trimebutine on intestinal motility and plasma motilin in the dog

In a previous report, trimebutine was shown to induce premature periods of phase III activity in fasting dogs, and its action was blocked by naloxone. In this study, we observed that trimebutine (5 mg X kg-1 iv) could induce premature phase IIIs in canine small intestine during interdigestive and digestive periods; trimebutine-induced phase IIIs were migrating along the small intestine faster than spontaneous activity fronts and; trimebutine-induced phase IIIs were accompanied by sharp rises in concentrations of plasma motilin. To further elucidate the trimebutine-stimulatory mechanism, we verified its effects on the release of various circulating peptides that influence intestinal motility: short-interval blood sampling during trimebutine infusion revealed that plasma motilin increases induced by trimebutine preceded the beginning of phase III in proximal duodenum; and gastrin and insulin postprandial releases were abolished by trimebutine. Therefore, trimebutine, by its simultaneous but opposite effects on various peptides that individually carry positive (e.g., motilin) or negative (e.g., gastrin and insulin) influences on the generation of activity fronts, could alter the equilibrium between stimulatory and inhibitory forces in such a way that, in some circumstances (e.g., postprandial period), stimulatory mechanisms become predominant.

Late increase in serum 1,25-dihydroxyvitamin D one month after surgery for adenomatous hyperparathyroidism

This study was designed to follow the evolution of serum 1,25(OH)2D after surgery for primary hyperparathyroidism. Ten patients were studied before and for up to 85 d after removal of a single parathyroid adenoma. Blood and 24 h urine were obtained at various time points, for the measurement of serum or urinary phosphate and calcium indices. Before surgery, serum calcium (2.91 +/- 0.06 mmol/l; mean +/- SEM), parathyroid hormone (354 +/- 47 pg/ml) and 1,25(OH)2D (61.2 +/- 7.8 pg/ml) were elevated while serum phosphate (1.01 +/- 0.07 mmol/l) tended to be low. Relative hypoparathyroidism was evident for up to 5 d after surgery with the lowest value for serum parathyroid hormone (41 +/- 16 pg/ml) on day 1, serum calcium (2.12 +/- 0.06 mmol/l) on day 3 and highest value for serum phosphate (1.41 +/- 0.13 mmol/l) on day 5. As expected, serum 1,25(OH)2D levels decreased to 35.9 +/- 4.2 pg/ml 24 h after surgery. Stabilization of serum and urinary parameters to normal values was seen between day 5 and day 27; the only exception was serum 1,25(OH)2D, which increased again at day 27 to 57.6 +/- 5.0 pg/ml, a value as high as that before surgery. It was still elevated at day 50 (58.3 +/- 4.3 pg/ml), but returned towards normal values in three out of four patients (44 +/- 3.9 pg/ml) by day 80. No variation in 25(OH)D or 24,25(OH)2D was seen throughout the study. 1,25(OH)2D values could be related to serum parathyroid hormone values before surgery (r = 0.659, P less than 0.05) but not after. The secondary increase in serum 1,25(OH)2D could not be related to variations in serum calcium, phosphate, parathyroid hormone or diet. Further studies will be required to explain this phenomenon.

Simple method for development of sensitive and specific antiinsulin antisera for laboratory use

Commercial sources provide good, though expensive antiinsulin antisera. We describe here a simple, fast and inexpensive method for the production of antiinsulin antisera. Purified pork insulin (Lente) was injected subcutaneously in oil/water/complete Freund adjuvant mixture. Three guinea pigs received 0.25 mg of insulin and three received 0.5 mg of insulin. Subsequent injections of the same dose were done 40 and 60 days later. Five animals developed antisera with titers superior to 1:10,000 40 days after the primary inoculation. Four out of five guinea pigs improved further their antibody titer after the 2nd and 3rd injection (p less than 0.0005). Good sensitivity was associated with titers superior to 1:50,000 and appeared only after the 2nd injection to improve further after the 3rd. Thus, four out of six animals developed antiinsulin antisera suitable for the radioimmunoassay (RIA). The antisera bound proinsulin on an equimolar basis with insulin while glucagon was not bound up to 100 ng/ml. The minimum detectable insulin concentration was about 12 pg (0.3 microU) at the optimum antiserum dilution. Six animals given a small dose of insulin (0.06 mg) developed antisera of a low titer and sensitivity, unsuitable for the RIA.

The thyroid nodule: evaluation of fine-needle biopsy

Sixty-three consecutive unselected patients with a solitary cold nodule of the thyroid were submitted to surgery. Prior to surgery they all had clinical evaluation and a fine-needle aspiration (FNA) biopsy of the nodule. Results of this study show that the FNA biopsy was correct in predicting cancer in 12 of 13 cancers for a sensitivity of 92%. When the nodule was benign, the FNA biopsy was right in 42 of the 50 benign nodules for a specificity of 84%. In comparison the clinical criteria alone were correct in suspecting only eight of the 13 cancers for a sensitivity of 62%, while correctly identifying 39 of the 50 benign nodules for a specificity of 72%. An association of the clinical criteria with the results of the FNA biopsy would have identified all the cancers in our group.

Insulin and insulin receptors in rodent brain

While insulin effects on the central nervous system (CNS) mediated through hypoglycaemia are well known, direct insulin effects on the CNS remain controversial. Recently, we found insulin receptors in all areas of the rat brain, with highest concentrations in the olfactory bulb, cerebral cortex and hypothalamus; all areas involved in feeding. Insulin receptors in brain were, by multiple criteria, similar to insulin receptors on classical target tissues for insulin, such as liver and fat. Insulin itself has been identified in the rat brain at concentrations on average ten times higher than in plasma. Highest concentrations were found in the olfactory bulb and hypothalamus. Brain insulin was indistinguishable from purified insulin by its behaviour in the radioimmunoassay, radioreceptor assay, bioassay and gel chromatography. In two experimental models representing extremes of plasma insulin concentrations (obese hyperinsulinaemic mice and diabetic insulinopenic rats) there were no significant changes in the concentration of insulin receptors in brain while liver receptors were modified in the expected way. This may reflect the protective influence of the blood-brain barrier or some special quality of brain insulin receptors. Insulin concentrations in brain were also unchanged in both models, which is probably indicative of the local synthesis of insulin. The role of insulin in the CNS is unknown. Besides well known metabolic actions of insulin, new roles can be postulated such as neurotransmission, neuromodulation and paracrine signalling.

Insulin and insulin receptors in rodent brain

While insulin effects on the central nervous system (CNS) mediated through hypoglycaemia are well known, direct insulin effects on the CNS remain controversial. Recently, we found insulin receptors in all areas of the rat brain, with highest concentrations in the olfactory bulb, cerebral cortex and hypothalamus; all areas involved in feeding. Insulin receptors in brain were, by multiple criteria, similar to insulin receptors on classical target tissues for insulin, such as liver and fat. Insulin itself has been identified in the rat brain at concentrations on average ten times higher than in plasma. Highest concentrations were found in the olfactory bulb and hypothalamus. Brain insulin was indistinguishable from purified insulin by its behaviour in the radioimmunoassay, radioreceptor assay, bioassay and gel chromatography. In two experimental models representing extremes of plasma insulin concentrations (obese hyperinsulinaemic mice and diabetic insulinopenic rats) there were no significant changes in the concentration of insulin receptors in brain while liver receptors were modified in the expected way. This may reflect the protective influence of the blood-brain barrier on some special quality of brain insulin receptors. Insulin concentrations in brain were also unchanged in both models, which is probably indicative of the local synthesis of insulin. The role of insulin in the CNS is unknown. Besides well known metabolic actions of insulin, new roles can be postulated such as neurotransmission, neuromodulation and paracrine signalling.

Insulin is ubiquitous in extrapancreatic tissues of rats and humans

Insulin has been detected, at levels higher than those in plasma, in a broad range of extrapancreatic tissues in both rats and humans. Rat liver insulin was shown to be indistinguishable from genuine insulin by radioimmunoassay, Sephadex chromatography, bioassay, and antibody neutralization. Liver insulin (like brain insulin) was unchanged in ob/ob mice, in rats treated with streptozotocin, or in fasted rats, despite marked alterations in pancreatic secretion of insulin and in liver content of insulin receptors. Insulin was found in cultured human IM-9 lymphocytes and cultured fibroblasts at concentrations greater than 100 times the levels in the media. IM-9 lymphocyte insulin also was shown to be indistinguishable from genuine insulin, by the same criteria used for liver insulin. The insulin concentration in cultured human cells was unaffected by depletion of insulin from the culture medium or by addition of beef insulin to the medium. The data suggest that a part, if not all, of the extrapancreatic tissue insulin is independent of plasma insulin and may be synthesized by the tissues themselves.

Concentrations of insulin and insulin receptors in the brain are independent of peripheral insulin levels. Studies of obese and streptozotocin-treated rodents

In view of the potent influences of the central nervous system on glucose metabolism and on its hormonal regulators, and our recent finding of insulin and insulin receptors throughout the central nervous systsem, we have examined extreme conditions of hyperinsulinemia (obese mice) and hypoinsulinemia (streptozotocin-treated rats) with respect to changes in brain insulin and receptor content. Sprague-Dawley rats given streptozotocin (100 mg/kg body wt) developed severe diabetes and by 48 h showed no change in brain insulin. Rats given 65 mg/kg streptozotocin also had severe diabetes, but survived longer. Both at 7 d and at 30 d after streptozotocin treatment there was no significant change in brain insulin or in brain content of insulin receptors, despite the fact that peripheral hepatic receptors were elevated and pancreatic insulin was markedly depleted. The obese mice were studied at 8-10 wk when peripheral plasma insulin concentrations were 50-fold elevated and receptors on peripheral target cells were reduced to congruent with40-50% of normal; brain insulin concentrations and receptor content were indistinguishable from those of thin littermates. Thus, brain insulin, which is typically 10 times higher than plasma insulin concentrations, and brain receptor content, which is equivalent to receptor content on peripheral tissues, appears to be regulated entirely independently of hormone and receptor in the periphery. These findings are consistent with the hypothesis that insulin in the central nervous system is synthesized by the neural elements, and plays a role in the central nervous system which is unrelated to peripheral glucose metabolism.

Identification of insulin in rat brain

Insulin concentrations in acid/ethanol extracts of the whole rat brain were on the average 25 times higher than plasma insulin levels. Brain insulin was indistinguishable from authentic pancreatic insulin, based on its behavior in radioimmunoassay, radioreceptor assay, and bioassay and its chromatographic pattern on Sephadex G-50 column chromatography. Insulin was found in all regions of the brain examined, but distribution was uneven. Some regions had insulin concentrations as much as 100 times higher than in plasma; levels at least 10 times higher were found in other regions. The role of insulin in the central nervous system is not clear at present but, because both insulin and insulin receptors are abundant in the central nervous system, an extensive physiological regulation of the central nervous system by insulin is proposed.

Insulin resistance, acanthosis nigricans, and normal insulin receptors in a young woman: evidence for a postreceptor defect

We have previously described a group of young females with virilization, acanthosis nigricans, insulin resistance, and markedly decreased binding of insulin to its receptor (syndrome of insulin resistance and acanthosis nigricans type A). The present report concerns a 15-yr-old female with clinical features indistinguishable from the type A patients, including virilization, acanthosis nigricans, and extreme resistance to endogenous and exogenous insulin. Insulin levels were 400-650 microU/ml while fasting and were over 2200 microU/ml when stimulated. Proinsulin was less than 10% of the total immunoassayable insulin. In distinct contrast to the type A patients, insulin receptors on cells from this patient were entirely normal on the basis of specificity, negative cooperativity, affinity, concentration, and interaction with antiinsulin receptor antibodies. These findings suggest the presence of an intracellular defect as the cause of the observed insulin resistance.