Effect of pioglitazone on body composition and bone density in subjects with prediabetes in the ACT NOW trial

AIMS

This study examined the effects of pioglitazone on body weight and bone mineral density (BMD) prospectively in patients with impaired glucose tolerance as pioglitazone (TZD) increases body weight and body fat in diabetic patients and increases the risk of bone fractures.

METHODS

A total of 71 men and 163 women aged 49.3 (10.7) years [mean (s.d.)]; body mass index (BMI), 34.5 (5.9) kg/m(2) were recruited at five sites for measurements of body composition by dual energy X-ray absorptiometry at baseline and at conversion to diabetes or study end, if they had not converted.

RESULTS

Mean follow-up was 33.6 months in the pioglitazone group and 32.1 months in the placebo group. Body weight increased 4.63 ± 0.60 (m ± s.e.) kg in the pioglitazone group compared to 0.98 ± 0.62 kg in the PIO group (p < 0.0001). Body fat rose 4.89 ± 0.42 kg in the pioglitazone group compared to 1.41 ± 0.44 kg, (p < 0.0001) in placebo-treated subjects. The increase in fat was greater in legs and trunk than in the arms. BMD was higher in all regions in men and significantly so in most. PIO decreased BMD significantly in the pelvis in men and women, decreased BMD in the thoracic spine and ribs of women and the lumbar spine and legs of men. Bone mineral content also decreased significantly in arms, legs, trunk and in the total body.

CONCLUSIONS

Pioglitazone increased peripheral fat more than truncal fat and decreased BMD in several regions of the body.

Determinants of glucose tolerance in impaired glucose tolerance at baseline in the Actos Now for Prevention of Diabetes (ACT NOW) study

AIMS/HYPOTHESIS

The aim of the study was to examine the determinants of oral glucose tolerance in 602 persons with impaired glucose tolerance (IGT) who participated in the Actos Now for Prevention of Diabetes (ACT NOW) study.

METHODS

In addition to the 602 IGT participants, 115 persons with normal glucose tolerance (NGT) and 50 with impaired fasting glucose (IFG) were identified during screening and included in this analysis. Insulin secretion and insulin sensitivity indices were derived from plasma glucose and insulin during an OGTT. The acute insulin response (AIR) (0-10 min) and insulin sensitivity (S(I)) were measured with the frequently sampled intravenous glucose tolerance test (FSIVGTT) in a subset of participants.

RESULTS

At baseline, fasting plasma glucose, 2 h postprandial glucose (OGTT) and HbA(1c) were 5.8 +/- 0.02 mmol/l, 10.5 +/- 0.05 mmol/l and 5.5 +/- 0.04%, respectively, in participants with IGT. Participants with IGT were characterised by defects in early (DeltaI (0-30)/DeltaG (0-30) x Matsuda index, where DeltaI is change in insulin in the first 30 min and DeltaG is change in glucose in the first 30 min) and total (DeltaI(0-120)/DeltaG(0-120) x Matsuda index) insulin secretion and in insulin sensitivity (Matsuda index and S(I)). Participants with IGT in whom 2 h plasma glucose was 7.8-8.3 mmol/l had a 63% decrease in the insulin secretion/insulin resistance (disposition) index vs participants with NGT and this defect worsened progressively as 2 h plasma glucose rose to 8.9-9.94 mmol/l (by 73%) and 10.0-11.05 mmol/l (by 80%). The Matsuda insulin sensitivity index was reduced by 40% in IGT compared with NGT (p < 0.005). In multivariate analysis, beta cell function was the primary determinant of glucose AUC during OGTT, explaining 62% of the variance.

CONCLUSION

Our results strongly suggest that progressive beta cell failure is the main determinant of progression of NGT to IGT.

Is adiposopathy (sick fat) an endocrine disease?

OBJECTIVE

To review current consensus and controversy regarding whether obesity is a 'disease', examine the pathogenic potential of adipose tissue to promote metabolic disease and explore the merits of 'adiposopathy' and 'sick fat' as scientifically and clinically useful terms in defining when excessive body fat may represent a 'disease'.

METHODS

A group of clinicians and researchers, all with a background in endocrinology, assembled to evaluate the medical literature, as it pertains to the pathologic and pathogenic potential of adipose tissue, with an emphasis on metabolic diseases that are often promoted by excessive body weight.

RESULTS

The data support pathogenic adipose tissue as a disease. Challenges exist to convince many clinicians, patients, healthcare entities and the public that excessive body fat is often no less a 'disease' than the pathophysiological consequences related to anatomical abnormalities of other body tissues. 'Adiposopathy' has the potential to scientifically define adipose tissue anatomic and physiologic abnormalities, and their adverse consequences to patient health. Adiposopathy acknowledges that when positive caloric balance leads to adipocyte hypertrophy and visceral adiposity, then this may lead to pathogenic adipose tissue metabolic and immune responses that promote metabolic disease. From a patient perspective, explaining how excessive caloric intake might cause fat to become 'sick' also helps provide a rationale for patients to avoid weight gain. Adiposopathy also better justifies recommendations of weight loss as an effective therapeutic modality to improve metabolic disease in overweight and obese patients.

CONCLUSION

Adiposopathy (sick fat) is an endocrine disease.

Hypoglycemia

Except in diabetic patients receiving insulin or sulfonylureas, hypoglycemia is a rare disorder. It is identified by modified Whipple's criteria consisting of neuroglycopenic symptoms, a blood glucose level equal to or less than 40 mg/dL, and relief of symptoms by glucose use. The sources of the body glucose are dietary intake, glycogenolysis, and [figure: see text] gluconeogenesis. The metabolism of glucose involves oxidation and storage as glycogen or fat. Causes of hypoglycemia include medications or toxins capable of decreasing blood glucose, disorders associated with fasting hypoglycemia, and postprandial hypoglycemic disorders. The most common type of hypoglycemia is insulin-induced hypoglycemia in diabetics. Insulinoma is rare; however, it is the most common hormone-secreting islet cell tumor. The diagnosis is made by the occurrence of hypoglycemia in the presence of symptoms of neuroglycopenia and inappropriately high levels of insulin and C-peptide. In hospitalized patients, the diagnosis is best made by prolonged fast. Most insulinomas are small and require invasive methods for precise localization. In surreptitious insulin use, hypoglycemia is associated with low plasma C-peptide. Postprandial hypoglycemia occurs in response to feeding and is generally caused by excessive insulin effect. It is seen in patients with postgastric surgery and rarely in early diabetes mellitus. Idiopathic postprandial hypoglycemia is rare and seems to be caused by subtle abnormalities of insulin response to food. Treatment of postprandial hypoglycemia consists of frequent small meals, with deletion of refined carbohydrate and increased protein intake. Primary treatment of insulinoma is surgical resection of the tumor.

Management of type 2 diabetes. Evolving strategies for treatment

Type 2 diabetes is the most prevalent form of diabetes, accounting for approximately 90% of cases. This article examines the current classification, diagnostic criteria for diabetes, and screening recommendations and provides a therapeutic strategy for improving glycemic control in patients with type 2 diabetes.

Adrenal androgen and glucocorticoid dissociation in premenopausal rheumatoid arthritis: a significant correlate or precursor to onset?

Controlled studies of adrenal steroids in premenopausal women with rheumatoid arthritis (RA) have revealed subtle and inconsistent decreases in glucocorticosteroid (GCS) function, but prominent deficiencies of adrenal androgens (AA). Such findings have suggested that hypoandrogenicity may predispose to RA in younger women. However, recent prospective studies of serum cortisol and dehydroepiandrosterone sulfate (DHEAS) levels before (x = 12 yrs) the onset of the disease (pre-RA) offer an alternative perspective. Significant dissociation of serum cortisol and DHEAS levels was found only in the subgroup of premenopausal women who developed RA before age 50. This subgroup alone had significant deficiency in serum DHEAS levels. Aggregate data imply that the documented deficits of DHEAS (and other AA) in such young females are a correlate of relative adrenal insufficiency, and that subtle GCS dysfunction may either contribute to development of RA in such young women as well as pubertal girls or may predispose to earlier onset of disease.

Comparative efficacy and potency of long-term therapy with glipizide or glyburide in patients with type 2 diabetes mellitus

BACKGROUND

Long-term studies on the comparative efficacy and relative potency of glipizide and glyburide are sparse and controversial.

METHODS

In a randomized prospective trial, we compared the effectiveness and relative potency of glipizide and glyburide over a 15-month period in 18 patients with type 2 diabetes mellitus (DM2) (9 on glyburide and 9 on glipizide) who were unresponsive to diet therapy. Glycemic control was assessed using 4 methods: 1) quarterly fasting plasma glucose (FPG), and 2-hour postprandial plasma glucose after a standard breakfast; 2) insulin and glucose response to Sustacal (test meal) challenge every 3 to 6 months; 3) quarterly hemoglobin A1c; and 4) intravenous glucose tolerance testing every 6 months to measure first and second phase insulin secretion. Patient characteristics were similar in each treatment group.

RESULTS

Similar doses of glipizide (11 mg/day) or glyburide (10 mg/day) resulted in comparable reduction of FPG and hemoglobin A1c and increase in first phase insulin response to intravenous glucose tolerance testing. There was greater reduction in FPG and 2-hour postprandial plasma glucose with glipizide than with glyburide in 6 months. Contrary to the Physicians' Desk Reference, but consistent with another short-term study, our long-term study demonstrated that glipizide and glyburide are equipotent at similar doses in controlling hyperglycemia in DM2.

CONCLUSIONS

Glipizide and glyburide are effective in controlling hyperglycemia with similar doses in DM2. Glipizide exhibits greater reduction in FPG and 2PPG at 6 months. Additional studies are needed to validate equipotency of these drugs.

Does syndrome X exist in hypertensive elderly persons with impaired glycemic control?

BACKGROUND

This report focuses on the glycemic state in relation to insulin and lipid levels of a cohort of elderly hypertensive persons to estimate the prevalence of syndrome X.

METHODS

A cross-sectional study was performed at the University of Tennessee, Memphis, and the General Clinical Research Center (GCRC) on 95 participants in the Trial of Nonpharmacologic Interventions in the Elderly (TONE) study who agreed to participate in an ancillary study. A standard oral glucose tolerance test (OGTT) with insulin and C-peptide levels and a fasting lipid profile were obtained.

RESULTS

In this sample of healthy elderly participants with hypertension who were taking an antihypertensive medication, 43 (45.3%) had normal glucose tolerance (NGT), 41 (43.2%) had impaired glucose tolerance (IGT), and 11 (11.6%) had undiagnosed non-insulin-dependent diabetes mellitus (NIDDM). Fasting hyperinsulinemia occurred in only one participant, who was in the IGT group. Hypertriglyceridemia and low high density lipoprotein (HDL) occurred in four persons, none of whom had hyperinsulinemia. Persons in the NIDDM and IGT groups had decreased beta cell function compared to persons in the NGT group, but did not have increased peripheral insulin resistance as estimated from the OGTT data.

CONCLUSIONS

Our data demonstrated that in this cohort of elderly hypertensive participants with a high prevalence of central obesity, impaired glycemic control was common, but was not associated with fasting hyperinsulinemia or peripheral insulin resistance. Furthermore, we conclude that syndrome X essentially did not occur in these participants and postulate that the primary etiology for their impaired glycemic control is beta cell dysfunction. Further research is needed to elucidate these relationships.

Racial differences in the correlation between gonadal androgens and serum insulin levels

OBJECTIVE

We previously demonstrated a direct correlation between serum insulin levels and gonadal androgens (testosterone and androstenedione) in a group of obese hyperandrogenic predominantly black women. Subsequent work by others in predominantly white women showed conflicting results. To examine these potentially important racial differences further, 14 premenopausal females from each ethnic group, of similar age, BMI, and waist-to-hip ratio, were studied.

RESEARCH DESIGN AND METHODS

We measured baseline gonadal androgens, dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), and leutinizing hormone (LH)/follicle-stimulating hormone ratio. Serum glucose, insulin, and C-peptide were measured at baseline and during a 2-h oral glucose tolerance test (area under the curve [AUC]). Insulin sensitivity was measured by glucose decrement during the first 15 min of an intravenous insulin tolerance test.

RESULTS

Simple correlation analysis revealed a significant direct correlation in blacks (but not whites) between gonadal androgens and AUC for glucose, insulin, and C-peptide. Race-by-covariate interaction models reinforced the simple correlation finding. Cholesterol level was also correlated to all androgens in blacks, but not in whites. We also found that whites had higher serum triglycerides and greater AUC glucose than blacks.

CONCLUSIONS

We conclude that there is a significant direct correlation between gonadal androgens and stimulated glucose, insulin, and C-peptide in blacks but not in whites. Thus, the previously reported direct correlation between gonadal hyperandrogenism and hyperinsulinemia may be a race-dependent phenomenon, hitherto an unreported observation. The implications of these findings are discussed.

Immunogenetic analysis suggests different pathogenesis for obese and lean African-Americans with diabetic ketoacidosis

OBJECTIVE

When presenting with diabetic ketoacidosis (DKA), lean and obese patients differ in their subsequent clinical course. Although lean patients tend to remain insulin dependent, most obese patients recover endogenous insulin secretion and discontinue insulin therapy. The aim of this study was to determine whether obese African-American patients with DKA could be determined to have type 1 or type 2 diabetes based on insulin secretion or the presence of immunological and genetic markers.

RESEARCH DESIGN AND METHODS

This was a prospective study that analyzed the clinical characteristics, insulin secretion indices, immunological markers (islet cell, GAD, ICA512, and insulin autoantibodies), and HLA susceptibility genes (DR/DQ) in 131 patients with DKA (77 obese and 54 lean), 51 obese patients with hyperglycemia but no DKA, and 25 nondiabetic subjects. All subjects were African-American. Beta-cell function was evaluated by the C-peptide response to glucagon (1 mg i.v.) within 48 h of resolution of DKA or hyperglycemia.

RESULTS

The acute C-peptide response was lower in obese DKA patients (1.0+/-0.1 ng/ml) than in obese patients with hyperglycemia (1.7+/-0.2 ng/ml, P < 0.01), but was higher than that in lean DKA patients (0.2+/-0.1 ng/ml, both P < 0.01). The overall prevalence of autoantibodies in obese subjects with DKA (17%) and obese subjects with hyperglycemia (16%) was lower than that in lean subjects with DKA (65%, P < 0.01). Obese patients with hyperglycemia and positive autoantibodies had lower rates of insulin secretion than those without antibodies. Regardless of body weight, all DKA patients with GAD autoantibodies carried the DQB1*0201 allele. However, there were no significant differences in HLA distribution between the three patient groups.

CONCLUSIONS

Our results indicate that most obese African-American patients with DKA have type 2 diabetes characterized by higher insulin secretion, the absence of autoimmune markers, and a lack of HLA genetic association. In contrast, most lean African-American patients with DKA have metabolic and immunological features of type 1 diabetes. At presentation, assessment of beta-cell function and determination of autoimmune markers allow for correct classification of diabetes in African-Americans with hyperglycemic crises.

Management of diabetic ketoacidosis

Diabetic ketoacidosis is an emergency medical condition that can be life-threatening if not treated properly. The incidence of this condition may be increasing, and a 1 to 2 percent mortality rate has stubbornly persisted since the 1970s. Diabetic ketoacidosis occurs most often in patients with type 1 diabetes (formerly called insulin-dependent diabetes mellitus); however, its occurrence in patients with type 2 diabetes (formerly called non-insulin-dependent diabetes mellitus), particularly obese black patients, is not as rare as was once thought. The management of patients with diabetic ketoacidosis includes obtaining a thorough but rapid history and performing a physical examination in an attempt to identify possible precipitating factors. The major treatment of this condition is initial rehydration (using isotonic saline) with subsequent potassium replacement and low-dose insulin therapy. The use of bicarbonate is not recommended in most patients. Cerebral edema, one of the most dire complications of diabetic ketoacidosis, occurs more commonly in children and adolescents than in adults. Continuous follow-up of patients using treatment algorithms and flow sheets can help to minimize adverse outcomes. Preventive measures include patient education and instructions for the patient to contact the physician early during an illness.

Prevalence of undiagnosed non-insulin-dependent diabetes mellitus and impaired glucose tolerance in a cohort of older persons with hypertension

OBJECTIVE

To determine the prevalence of undiagnosed non-insulin-dependent diabetes mellitus (NIDDM) and impaired glucose tolerance (IGT) in a cohort of older persons with hypertension. To examine the usefulness of screening for NIDDM in this study population.

DESIGN

Cross-sectional study.

SETTING

University of Tennessee, Memphis and the General Clinical Research Center (GCRC).

PATIENTS

Ninety-five participants in the Trial of Nonpharmacologic Interventions in the Elderly (TONE) study who agreed to participate in an ancillary study.

MEASUREMENTS

A standard oral glucose tolerance test (OGTT) with insulin and C-peptide levels was performed before the beginning of the TONE intervention.

RESULTS

In this cohort, 43 participants (45.3%) had normal glucose tolerance (NGT), 41 (43.2%) had IGT, and 11 (11.6%) had undiagnosed NIDDM. The positive predictive value for NIDDM of a fasting glucose > or = 115 mg/dL in our participants was 57%. Hyperinsulinemia occurred in only one participant, a subject in the IGT group.

CONCLUSIONS

Our data demonstrate that undiagnosed NIDDM is common in our cohort of older persons who are being treated for essential hypertension and that impaired glucose tolerance may be more common than in the general population of the same age. Further, our data show that the vast majority of this older, obese, hypertensive cohort did not have fasting hyperinsulinemia. We also infer that a fasting glucose alone has a low positive predictive value for screening of NIDDM in our older cohort. As the prevalence of NIDDM and impaired glucose tolerance in older hypertensive patients in the general population is unknown, we believe that further investigation is needed to characterize the relationship of hypertension, glycemic status, and hyperinsulinemia in the general population.

Hyperglycemic crises in urban blacks

BACKGROUND

The hospital admission and mortality rates of patients with diabetic emergencies, such as diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar nonketotic syndrome (HHNS), are higher in black patients than in white patients with diabetes. However, there is limited data describing the precipitating events and response to treatment in black patients. Analysis of their clinical characteristics and response to medical therapy is needed to evaluate the impact of programs designed to reduce the development of these acute metabolic complications.

METHODS

A prospective evaluation was conducted of 144 consecutive patients with DKA and 23 patients with HHNS admitted to a large inner-city hospital between July 1993 and October 1994.

RESULTS

In patients previously diagnosed as having diabetes, poor compliance with insulin therapy was the major precipitating cause for DKA (49%) and HHNS (42%). Alcohol or cocaine abuse was a contributing factor for noncompliance and was present in 35% and 13% of patients with DKA and in 44% and 9% of patients with HHNS, respectively. Newly diagnosed diabetes accounted for 17% of patients with DKA and HHNS. Obesity (body mass index > 28 kg/m2 [the weight in kilograms divided by the square of the height in meters]) was present in 29% of patients with DKA and in 17% with HHNS and was most common in patients with DKA who were newly diagnosed as having diabetes (56%). Patients were treated by residents, who used a low-dose insulin protocol with an algorithm for insulin adjustment in 88 of 144 patients with DKA and 14 of 23 patients with HHNS. Although there was no difference in mortality rates or time needed to correct hyperglycemia or ketoacidosis, the use of the protocol significantly reduced the risk of hypoglycemia (5%) compared with patients treated without a protocol (23%) (P < .01).

CONCLUSIONS

In urban black patients, poor compliance with insulin therapy was the main precipitating cause of acute metabolic decompensation, and substance abuse was a significant contributing factor for noncompliance. Obesity is common in black patients with DKA; it was present in more than half of those with newly diagnosed diabetes. Improved patient education and better access to medical care might reduce the development of these hyperglycemic emergencies.

NIDDM: new aspects of management

Patients over age 40 should be made aware of the triad of risk factors for the disease and taught to recognize common signs and symptoms. Those with high-risk profiles should be tested regularly and counseled regarding preventive and therapeutic strategies. For obese patients whose weight cannot be brought under control with diet and exercise alone, a trial of anorectic agents should be considered.

Differing effects of pancreas-kidney transplantation with systemic versus portal venous drainage on cholesteryl ester transfer in IDDM subjects

OBJECTIVE

Cholesteryl ester transfer (CET) is accelerated in patients with IDDM treated with conventional (subcutaneous) insulin therapy (CIT) and a number of other disorders associated with premature cardiovascular disease. We have shown that in IDDM this disturbance is closely linked to iatrogenic hyperinsulinemia (HI), because it was reversed when insulin was administered by the intraportal (i.p.) route. In this study, we sought to determine whether HI after successful pancreas-kidney transplantation (PKT) has the same adverse effect on CET.

RESEARCH DESIGN AND METHODS

CET was measured by both mass and isotopic assays and compared in two groups of euglycemic non-insulin-requiring IDDM PKT patients with either systemically draining allografts and persistent HI or grafts with portal vein anastomoses that were normoinsulinemic (PK-P). A third group of eight nondiabetic kidney transplant (KT) patients receiving the same immunosuppressive drugs served as control subjects.

RESULTS

CET in pancreas-kidney transplantation subjects with systemic venous drainage (PK-S) was increased (P < 0.001) to the same level we have reported previously in IDDM patients receiving CIT and was significantly higher (P < 0.001) than in those subjects with PK-P. CET in the PK-P group did not differ from that of the KT control patients.

CONCLUSIONS

CET is affected by variations in systemic insulin levels in pancreas transplant patients with allografts that have differing venous drainage. Because high systemic insulin levels are linked to the activation of (ET, euglycemic HI IDDM pancreas allograft recipients may continue to be at high risk for macrovascular complications.

Results of pancreas transplantation with portal venous and enteric drainage

PURPOSE

The standard method for pancreatic transplantation involves drainage of exocrine secretions into the urinary bladder with venous outflow into the systemic circulation. Despite the high success rate associated with this approach, it often leads to complications, including chemical cystitis, reflux pancreatitis, metabolic acidosis, and hyperinsulinemia. The authors developed a new technique of pancreatic transplantation with portal drainage of endocrine secretions and enteric drainage of exocrine secretions (PE), which theoretically should be more physiologic.

PROCEDURES

All patients were insulin-dependent diabetics with end-stage renal disease who underwent combined kidney-pancreas transplantation. Between 1990 and 1994, 19 patients have been transplanted using intraperitoneal placement of the pancreas allograft with exocrine drainage into a Roux-en Y loop and venous drainage into the portal circulations (PE). A comparison group of all patients undergoing standard systemic-bladder (SB) transplantation between April 1989 and March 1993 (n = 28) also was studied. Patient follow-up ranges from 6 months to 5 years for the SB patients (mean = 2.5 years) and 6 months to 4 years for the PE patients (mean = 1.6 years). Routine follow-up includes documentation of the clinical course and detailed endocrine studies.

FINDINGS

Patient and graft actuarial survival at 1 and 3 years is no different for SB and PE patients. Urinary tract infections occurred in 89.3% of the SB patients (2.8/patient) versus 26.3% of the PE patients (0.25/patient, p < or = 0.0001). None of the PE patients experienced hematuria compared with 53.6% of the SB patients (p < or = 0.0001); however, two PE patients had melanotic episodes. The incidence of urinary retention and reflux pancreatitis was 32.1% versus 5.3% (p < or = 0.028) for SB and PE groups, respectively. Patients in the SB group required sodium bicarbonate therapy (mean = 55 mEq/day) although no PE patient required routine therapy; despite this, SB patients experienced more episodes of acidosis (44 vs. 5). Endocrine studies indicate no difference in glycosylated hemoglobin or fasting and stimulated glucose values throughout the follow-up period. In contrast, hyperinsulinemia was evident in both fasting and stimulated tests for the SB patients, with values consistently two- to fivefold higher than those of the PE group.

CONCLUSIONS

These results indicate that PE and SB pancreas transplantation are equivalent in terms of patient and graft survival and suggest that the PE approach is associated with a decreased incidence of metabolic and bladder-related complications. In addition, the PE approach eliminates the state of peripheral hyperinsulinemia that characterizes the SB procedure. Continued follow-up will be necessary to determine if long-term outcomes will differ for patients with PE and SB grafts.

Diabetic ketoacidosis

This article reviews the pathogenesis of diabetic ketoacidosis (DKA) and provides a rational approach to the management of patients with DKA. The therapeutic discussion includes the use of low-dose insulin, no bicarbonate, or phosphate therapy on the majority of DKA patients, based on numerous prospective randomized studies. The article also discusses controversial subjects such as the use of hypotonic versus isotonic saline with and without colloids, hydration of subjects before insulin therapy, and admission of DKA patients to the general ward versus emergency ward versus intensive care unit. A concise, simple protocol is also presented as a suitable reference for management of patients with DKA.

Genetic and immunological markers of insulin dependent diabetes in Black Americans

ICA and GAD65 autoantibody profiles and HLA-DR and DQ analysis were performed on 43 Black juvenile onset IDDM patients and 34 unrelated Black controls from Tennessee, USA. 75% of patients were positive for GAD65 autoantibodies but only 53% had ICA; 39% both ICA and GAD65 antibodies. The strongest HLA association was with the DR3 haplotype DRB1*03 DQA1*0501 DQB1*0201 (63% of patients v 12% of controls RR = 13.0, p < 0.00002). DRB1*04 DQA1*0301 DQB1*0302, associated with IDDM in Caucasians but rare in Negroids, occurred in 27% of patients and 6% of controls (RR = 5.9, p < 0.04). All patients carried DQB1*0302 or DQB1*0201. DQB1*0602 was significantly reduced in patients (2.4% v 41%, RR = 0.036, p < 0.008) and DRB1*1501 was absent in patients (0% v 35%). The frequency of GAD65 autoantibodies in Black American IDDM patients is comparable to that in Caucasians; however ICA positivity is reduced. GAD65 antibodies may therefore be a more sensitive serological test to identify individuals in the Black American general population for markers associated with increased risk of developing IDDM. Current screening methods for predicting preclinical IDDM in Caucasians relies on a combination of immune and HLA markers of IDDM; studies of these markers in the Black Americans will make it possible to extend these options to additional genetically diverse populations.

Evidence for a defect in insulin metabolism in hyperandrogenic women with polycystic ovarian syndrome

It has been well established that the hypertestosteronemia of patients with polycystic ovarian syndrome (PCO) is associated with hyperinsulinemia and insulin resistance. We have recently noted a disparity between serum levels of insulin and C-peptide in certain hypertestosteronemic women with PCO and hypothesized a possible association between testosterone and insulin metabolism. Therefore, we have studied insulin clearance (baseline steady-state ratios of C-peptide to insulin) in 15 obese PCO women, 12 weight-matched controls (OC), and nine lean controls (LC), and examined the interactions of testosterone and insulin metabolism by examining the correlations between testosterone and insulin clearance and by studying the direct in vitro actions of testosterone on T-lymphocyte insulin binding and degradation. We found that the C-peptide to insulin ratio at baseline and T-lymphocyte insulin degradation of the PCO group were twofold below the LC and OC values. Basal C-peptide to insulin ratios and insulin-degradative activities were significantly and negatively interrelated (r = .56, P < .01), and both of these parameters were highly correlated (P < .01) with basal testosterone levels (r = .49 for basal C-peptide to insulin and r = -.61 for insulin degradation). In experiments where testosterone was added to cell cultures, insulin degradation was impaired in a biphasic fashion. We conclude that (1) elevated testosterone levels may contribute to impairments in insulin metabolism, and (2) the hyperinsulinemia of hyperandrogenic women may occur in part from defects in insulin clearance and peripheral tissue insulin degradation.

Enhanced adrenocortical activity as a contributing factor to diabetes in hyperandrogenic women

The high incidence of non-insulin-dependent diabetes mellitus (NIDDM) in women with polycystic ovarian syndrome (PCO) is believed to occur secondary to the insulin resistance associated with their androgenicity. In the present study, we have examined the interrelationships between glucose tolerance, androgenicity, and various in vivo and in vitro parameters of insulin sensitivity in 11 obese PCO patients with NIDDM, 14 PCO patients without diabetes, and 14 weight-matched controls. Both groups of PCO patients were hypertestosteronemic, hyperinsulinemic, and insulin-resistant when compared with a group of weight-matched controls. However, PCO patients with NIDDM differed from those without diabetes in that they had elevated basal and corticotropin-stimulated adrenal steroids (cortisol, dehydroepiandrosterone [DHEA], dehydroepiandrosterone sulfate [DHEAS]). The hyperglycemia of our diabetic patients was not related to their elevated testosterone levels or to their degree of insulin resistance, but was significantly and positively correlated with adrenal hypersecretion, which in turn was associated with postreceptor defects in insulin action. These findings would suggest that enhanced adrenocortical activity may be an important factor underlying the development of NIDDM in women with PCO.

Case report: amelioration of insulin resistance in diabetes with dehydroepiandrosterone

In hyperandrogenic females, the ratio of dehydroepiandrosterone (DHEA) to testosterone may be an important determinant of insulin sensitivity. This study involved changes in insulin sensitivity and glucose metabolism with therapeutic manipulation of DHEA (S)/testosterone in a female patient with non-insulin-dependent diabetes and hyperandrogenism. Therapeutic intervention included 1-month treatment with 0.25 mg dexamethasone at bedtime and 1-month dexamethasone + DHEA. Insulin sensitivity and glucose tolerance were assessed before and after each treatment regimen by examining: 1) fasting and oral glucose tolerance test glucose and insulin levels, 2) hypoglycemic response to intravenous insulin, and 3) erythrocyte insulin receptor binding. With dexamethasone alone, DHEAS, testosterone, and their ratio were reduced with a concomitant increase (30%) in oral glucose tolerance test insulin levels and a decrease (33%) in erythrocyte insulin binding. With DHEA + dexamethasone, the ratio of DHEAS/testosterone increased 16-fold along with a marked improvement in insulin sensitivity, as determined by a more than 30% reduction in fasting and oral glucose tolerance test insulin levels, a threefold stimulation of the rate of glucose disappearance with intravenous insulin, and a 30% increase in insulin binding. DHEA improved insulin sensitivity and reduced fasting and oral glucose tolerance test glucose levels and ameliorated the diabetic state. The ratio of DHEAS/testosterone is an important regulator of insulin sensitivity and glucose tolerance and that DHEA therapy may be beneficial in the treatment of certain forms of insulin resistance.

Opposing actions of dehydroepiandrosterone and testosterone on insulin sensitivity. In vivo and in vitro studies of hyperandrogenic females

It has been hypothesized that the androgens testosterone and dehydroepiandrosterone (DHEA) may have opposing actions on insulin sensitivity. To test this hypothesis, we selected patients with polycystic ovary syndrome (PCO) and hypertestosteronemia and a group of individuals with adrenal hyperplasia (AH) and elevated DHEA and studied their 1) insulin and glucose responses to a 75-g oral glucose tolerance test, 2) insulin resistance by hypoglycemic responses to a standard dose of intravenous (IV) insulin, and 3) insulin binding and pyruvate dehydrogenase (PDH) responsiveness to insulin in phytohemagglutinin (PHA)-activated T lymphocytes. PCO patients exhibited elevated basal and glucose-challenged insulin levels and had blunted hypoglycemic responses to IV insulin. Conversely, AH patients had hypoglycemic responses to IV insulin significantly greater than and basal and glucose-challenged insulin levels lower than the PCO patients and weight-matched control subjects. In vitro, T-lymphocyte insulin binding of the PCO patients was 40-60% below control values; in AH patients, insulin binding and PDH insulin sensitivity were above those of the control subjects. Testosterone levels in all study subjects were negatively correlated to T-lymphocyte insulin binding and positively correlated to basal insulin, insulin area under the curve (AUC), and insulin-glucose indices. DHEA levels were positively correlated to insulin binding and inversely related to basal insulin, insulin AUC, and insulin-glucose indices. In all instances, the parameters of insulin sensitivity were more strongly correlated to individuals' ratios of DHEA to testosterone than to either of these androgens alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of adrenal and gonadal androgens in insulin action and metabolism

In a previous report we found extreme hyperinsulinemia associated with high testosterone levels in patients with polycystic ovarian syndrome (PCO) and normal insulin levels in a small group of patients with elevated dehydroepiandrosterone (DHEA). From these observations, we hypothesized that DHEA and testosterone may have opposing actions on insulin sensitivity. To test this hypothesis, we studied insulin sensitivity in vivo and in vitro in a) obese PCO women with elevated testosterone, b) obese patients with adult-onset adrenal hyperplasia (AH) and high levels of DHEA, c) weight-matched obese controls, and d) lean controls. Insulin sensitivity was determined by insulin responses to a standard OGTT, hypoglycemic responses to an IV insulin tolerance test (ITT), red blood cell (RBC) insulin binding and receptor kinase activity, and phytohemagglutinin (PHA)-activated T-lymphocyte (T-cell) insulin binding and PDH insulin sensitivity. In PCO patients, we found that basal and glucose-challenged insulin levels were significantly greater than, and hypoglycemic responses to IV insulin, significantly lower than, weight-matched control values. However, AH patients had insulin values significantly below, and hypoglycemic responses significantly above, those of the weight-matched controls. Their values were, in fact, comparable to those observed for the lean control subjects. Similar findings were observed with insulin binding and PDH insulin sensitivity. Insulin sensitivity in all study subjects was found to be negatively correlated to testosterone and positively correlated to DHEA and, more significantly, to the ratio of DHEA/testosterone. These data would suggest that, in females, DHEA and T may have opposing actions on insulin sensitivity. We conclude that in females insulin sensitivity in vivo and in vitro is modulated, at least in part, by the ratios of DHEA to testosterone.

Pseudonormoglycemia in diabetic ketoacidosis with elevated triglycerides

A 24-year-old newly diagnosed male patient with diabetes presented with diabetic ketoacidosis (DKA) (pH 7.16, HCO3 6.0) and extreme hypertriglyceridemia (239.35 mmol/L). The diagnosis of DKA was delayed because of the apparent depression of the true serum glucose (to 11 mmol/L). He was treated with intravenous (IV) insulin and rehydration, which normalized his pH, HCO3, and triglyceride levels. To the authors' knowledge, this is both the highest triglyceride level recorded and the first report of a high triglyceride level as the apparent cause of a factitiously low glucose level.

Bimodal correlation between the circulating insulin level and the production rate of dehydroepiandrosterone: positive correlation in controls and negative correlation in the polycystic ovary syndrome with acanthosis nigricans

The objective of this study was to define the relationship among the circulating insulin level (IRI), the MCR of dehydroepiandrosterone (MCR-D), and the production rate of DHEA (PR-D) in 10 women with the polycystic ovary syndrome and acanthosis nigricans (PCOS-AN). Seven normal weight and 10 obese women served as controls. Measurement of the MCR-D and PR-D was accomplished by iv saline infusion (0.9% NaCl solution) on day 1 as a control and a 4-h iv dehydroepiandrosterone (unlabeled) infusion (1 mg/h) was performed on day 2. Mean MCR-D was more than 2-fold higher in the obese controls compared to the normal weight controls. However, the plasma concentration of DHEA(PC-D) was not significantly different in the normal and obese control women, since the PR-D was increased proportionately to the MCR-D. The MCR-D and the PR-D were coupled through insulin in the control women, and their correlation coefficients with IRI were positive and identical (0.77 and 0.73, respectively). In contrast, IRI was negatively correlated with PR-D in the PCOS-AN women. Also, unlike the control women, there was minimal or no change in the MCR-D across a broad range of IRI in the PCOS-AN women. Thus, the MCR-D and PR-D were not coupled in these women.

Sensitivity of pyruvate dehydrogenase to insulin in activated T lymphocytes. Lack of responsiveness to insulin in patients with polycystic ovarian disease and diabetes

Using phytohemagglutinin-activated T lymphocytes, we studied possible mechanisms responsible for insulin resistance in patients with polycystic ovarian disease (PCO) and acanthosis nigricans (AN) by examining insulin binding to erythrocytes and activated T lymphocytes and T-lymphocyte pyruvate dehydrogenase (PDH) responsiveness to insulin in three groups. These groups of subjects consisted of six PCO-AN patients with normal glucose tolerance, six PCO-AN patients with mild non-insulin-dependent diabetes mellitus (NIDDM), and six weight-matched control subjects. We found that insulin binding to both erythrocytes and activated T lymphocytes was significantly lower in PCO and PCO-NIDDM patients than control subjects but did not differ between the PCO groups. Insulin binding to erythrocytes and T lymphocytes varied inversely with basal insulin. In activated T lymphocytes of PCO-NIDDM patients, PDH responsiveness to both submaximal and maximal insulin concentrations was impaired, the extent of which varied in proportion to their degree of carbohydrate intolerance. In contrast, PDH responsiveness to maximal amounts of insulin in T lymphocytes of PCO patients without NIDDM was similar to the weight-matched control subjects. These data may suggest that lesions at the level of the receptor are primarily responsible for insulin resistance in patients with PCO but that both receptor and postreceptor defects (i.e., PDH responsiveness to insulin) contribute to the insulin-resistant state of PCO patients with NIDDM.

Identification of insulin intermediates and sites of cleavage of native insulin by insulin protease from human fibroblasts

We have studied the time sequence degradation of native insulin by insulin protease from human fibroblast using multiple steps involving purification of the products by high performance liquid chromatography, determination of peak composition by amino acid sequence analysis, and confirmation of structure by mass spectrometry and thus elucidated the sites of cleavage of insulin by human insulin protease. We observed that as early as 0.5 min of incubation, three major new peptide peaks, intact insulin, and four smaller peptide peaks can be detected. The major peptides are portions of the insulin molecule, with the amino ends of the A and B chains or the carboxyl ends of the A and B chains still connected by disulfide bonds. Peptide peak I is A1-13-B1-9. Peptide peak II is A1-14-B1-9. Peptide peak III is A14-21-B14-30. The smaller peptide peaks are A14-21-B17-30, A15-21-B14-30, A15-21-B10-30, and A14-21-B10-30. The major peptide bond cleavage sites therefore consist of A13-14, A14-15, B9-10, B13-14, and B10-17. With longer incubation times, peptide peak II appears to lose the A14 tyrosine to form peptide peak I. This peptide I, which is the amino end of the A and B chains, is not further degraded even after 1.5 h of incubation. With longer incubation times, the peptides containing the carboxyl ends of the A and B chains are further degraded to form products from cleavage at the A18-19, B14-15, B25-26, and a small amount of A19-20, B10-11, and B24-25 cleavage and the emergence of 2-5-amino acid peptide chains, tyrosine, alanine, histidine, and leucine-tyrosine. We conclude, based on the three-dimensional structure of insulin, that human insulin protease recognizes the alpha-helical regions around leucine-tyrosine bonds and that final degradation steps to small peptides do not require lysosomal involvement.

Diabetic ketoacidosis and hyperosmolar hyperglycemic nonketotic coma

Diabetic ketoacidosis and hyperosmolar hyperglycemic nonketotic coma are two of the most common acute complications of diabetes. The pathophysiologic changes that occur in both disease states represent an extreme example of the super-fasted state. The physiology of the fed and fasted state, evaluation, therapeutic issues, recommendations for therapy, immediate follow up care, and complications of therapy are reviewed for both syndromes.

Divergent correlations of circulating dehydroepiandrosterone sulfate and testosterone with insulin levels and insulin receptor binding

We evaluated the insulin response to a standard oral glucose tolerance test (OGTT) and in vitro insulin binding to erythrocytes (RBC) in 26 women from 3 groups: Group NW, normal women (n = 11); Group DS, women (n = 9) with elevated serum DHEAS concentrations, greater than 400 micrograms/dl (greater than 10.84 mumol/L); and Group IR, women (n = 6) with elevated basal plasma insulin concentrations (IRI). There was a significant linear correlation between the area under the insulin response curve (IRI-AUC) and serum testosterone (T) (r = 0.78, p = 0.0001). Using stepwise multiple linear regression, IRI-AUC was characterized as a function of both serum T and DHEAS; positively with T and negatively with DHEAS. In vitro (n = 17), there was a positive correlation between RBC-insulin binding and serum DHEAS (r = 0.54, p = 0.029) and a negative correlation between RBC-binding and T (r = -0.57, p = 0.017). We conclude that DHEAS may enhance insulin binding and action and that DHEAS and T have divergent functional relationships with IRI. DHEAS and T may therefore exert opposing effects on insulin secretion and action.

Increased insulin binding of erythrocytes and insulin sensitivity in adrenal insufficiency

We have studied 125I-insulin binding to erythrocytes (RBC) in five patients with hypoadrenocortisolism, and compared to 17 normal subjects and in nine patients with Cushing's syndrome. In another study insulin sensitivity index (ISI) was measured by the IV insulin tolerance test in four patients with hypoadrenocortisolism (1.82 +/- 0.15 mg/dL/min), and compared to 19 normal subjects and 23 patients with Cushing's syndrome (1.56 +/- 0.1 mg/min/dL). Mean insulin binding in hypocortisolism was 17.9 +/- 0.7%, and was significantly higher (P less than .01) than in normal subjects (12.0 +/- 1.4%) and was significantly (P less than .001) decreased toward normal (11.8 +/- 1.47) during replacement therapy. Increased binding in untreated hypoadrenocortisolism was due to elevated high affinity site receptor concentration as compared to the treated patients (0.10 +/- 0.015 v 0.053 +/- 0.003 nmol/L,P less than .01). These results suggest that increased insulin binding in chronic hypoadrenocortisolism may be attributed to increased insulin binding to the receptor, which can revert to normal by replacement therapy. The role of increased insulin binding to increased insulin sensitivity in hypoadrenocortisolism is discussed.

Combined therapy of insulin and tolazamide decreases insulin requirement and serum triglycerides in obese patients with noninsulin-dependent diabetes mellitus

Insulin requirements, C-peptide levels, and serum lipids have been assessed in 12 obese, insulin-requiring (greater than 60 U/day) patients with type II diabetes mellitus, in a randomized crossover fashion with two treatment regimens: NPH alone and combined NPH and tolazamide, over a period of 3 months each, with maintenance of weight and glycemic control (HgA1, 2hpp and mean 24h glucose profile) at comparable levels. Serum cholesterol improved in both groups compared to their respective baseline values (p less than 0.05). In addition, serum triglyceride was lower (p less than 0.05) in the combined therapy as compared with NPH alone therapy. Insulin requirements were decreased by 23% (p less than 0.002) in the combined therapy group, without significant change in weight, glycemic control, or C-peptide levels. However, C-peptide increments in the combined therapy group were significantly higher than the baseline by 70% (p less than 0.02). NPH plus tolazamide therapy as compared with NPH alone lowers insulin requirement in obese, type II diabetic women without significant alteration in glycemic control, possibly by an increased tissue sensitivity to insulin, and decreases serum triglyceride levels.

Glyburide-induced hepatitis

Drug-induced hepatotoxicity, although common, has been reported only infrequently with sulfonylureas. For glyburide, a second-generation sulfonylurea, only two brief reports of hepatotoxicity exist. Two patients with type II diabetes mellitus developed an acute hepatitis-like syndrome soon after initiation of glyburide therapy. There was no serologic evidence of viral infection, and a liver biopsy sample showed a histologic pattern consistent with drug-induced hepatitis. Both patients recovered quickly after stopping glyburide therapy and have remained well for a follow-up period of 1 year. Glyburide can produce an acute hepatitis-like illness in some persons.

Maintenance of normal circulating levels of delta 4-androstenedione and dehydroepiandrosterone in simple obesity despite increased metabolic clearance rates: evidence for a servo-control mechanism

To study the effect of obesity on the metabolism of adrenal androgens not bound to testosterone-estradiol-binding globulin, the MCRs of delta 4-androstenedione (A) and dehydroepiandrosterone (DHEA) were determined using constant infusion of unlabeled steroids to steady state in 8 normal weight and 19 obese nonhirsute eumenorrheic women. The blood production rates (PR) were calculated as the product of the MCR and the 24-h integrated serum concentrations (IC). The mean MCR and PR of A and DHEA were significantly higher in the obese women than in the normal weight women. There was, however, no difference in the mean IC of each androgen in the 2 groups. The MCR and PR of A and DHEA were each correlated with the body mass index (BMI; kilograms per m2). The MCR and PR of A and the MCR of DHEA were also correlated with the ratio of waist circumference to hip circumference (WHR). However, the PR of DHEA was not correlated with WHR. There was no correlation between the IC of either androgen and BMI or WHR. However, partial correlation analysis revealed that correction of the BMI for WHR resulted in a significant negative correlation between BMI and IC of A. We conclude that the MCR and PR of A and DHEA were increased in obese nonhirsute eumenorrheic women; there was a strong correlation between BMI and the MCR and PR of A and DHEA; upper segment obesity, as measured by WHR, was correlated with the MCR and PR of A and the MCR of DHEA, but not with the PR of DHEA; and circulating DHEA and A were maintained at normal levels in the obese eumenorrheic women despite an increase in the MCR, which suggests that a servo-mechanism is operative which registers the body size and adjusts the PR according to the MCR.

Reduction of hyperinsulinemia and insulin resistance by opiate receptor blockade in the polycystic ovary syndrome with acanthosis nigricans

We previously reported that circulating beta-endorphin levels are increased in obese hirsute women and that plasma immunoreactive insulin (IRI) levels are increased in proportion to the degree of hyperandrogenism in women with the polycystic ovary (PCO) syndrome. We, therefore, tested the hypothesis that endogenous opiates are at least partially responsible for the hyperinsulinemia and insulin resistance in this syndrome. In the first study, acute naloxone administration significantly reduced the plasma IRI response and IRI/glucose ratio in three euglycemic obese women with PCO and acanthosis nigricans (AN) and marked insulin resistance, but did not alter the glucose response. Naloxone had no effect on these parameters in the normal weight control subjects. In the second study, nalmefene, a new, orally active opiate antagonist, reduced IRI and the IRI/glucose ratio in four women with PCO-AN and marked hyperinsulinemia in a randomized, double blind, crossover protocol. We conclude that endogenous opiates are at least partially responsible for the hyperinsulinemia and insulin resistance in PCO-AN.

Bicarbonate therapy in severe diabetic ketoacidosis

Twenty-one adult patients with severe diabetic ketoacidosis entered a randomized prospective protocol in which variable doses of sodium bicarbonate, based on initial arterial pH (6.9 to 7.14), were administered to 10 patients (treatment group) and were withheld from 11 patients (control group). During treatment, there were no significant differences in the rate of decline of glucose or ketone levels or in the rate of increase in pH or bicarbonate levels in the blood or cerebrospinal fluid in either group. Similarly, there were no significant differences in the time required for the plasma glucose level to reach 250 mg/dL, blood pH to reach 7.3, or bicarbonate level to reach 15 meq/L. We conclude that in severe diabetic ketoacidosis (arterial pH 6.9 to 7.14), the administration of bicarbonate does not affect recovery outcome variables as compared with those in a control group.

Phytohemagglutinin (PHA) activated human T-lymphocytes: concomitant appearance of insulin binding, degradation and insulin-mediated activation of pyruvate dehydrogenase (PDH)

Binding and degradation of A14125I-Insulin as well as the effect of insulin on pyruvate dehydrogenase (PDH) activation were studied in non-stimulated and phytohemagglutinin (PHA)-stimulated thymic-derived lymphocytes (T-lymphocytes) of man under varying conditions of time, temperature, and cell concentration. The nonstimulated viable T-lymphocytes exhibited neither binding, degradation, nor PDH activation in response to insulin. With PHA stimulation, a time and temperature-dependent binding was noted in T-lymphocytes which paralleled the appearance of cell-associated insulin degrading activity. Concomitant with the emergence of insulin binding and degrading activities in these cells, PDH activation was observed which was responsive to as little as 5.0 microU/ml of insulin. We conclude that in PHA-activated T-lymphocytes of man the process of insulin binding and degradation is closely related to insulin sensitive activation of PDH. These activated cells may serve as a useful model in which to study insulin binding and processing, as well as effects of insulin on postreceptor events.

The effect of inhibitors of insulin processing on generation of insulin intermediate products from human fibroblast as detected by high performance liquid chromatography (HPLC)

To assess the role of various modulators of insulin processing on cell-associated A14-125I-insulin intermediates in human fibroblasts, we have studied the effect of N-ethylmaleimide (NEM), chloroquine, bacitracin, dansylcadavarine, and phenylarsine oxide on generation of these intermediate products with the use of HPLC. NEM completely inhibited generation of intermediate peaks or iodotyrosine. Chloroquine inhibited conversion of A14-125I-insulin to iodotyrosine by about 75 percent and the remaining A14-125I-insulin was not susceptible to acid wash. Bacitracin, dansylcadavarine, and phenylarsine oxide, on the other hand, stimulated formation of intermediate products with concomitant inhibition of iodotyrosine formation. We conclude that there are at least three components of insulin degradation in human fibroblasts. These include the sulfhydryl group inhibitor-sensitive, the intracellular chloroquine-sensitive, and membrane site inhibitor-sensitive components.

Characterization of insulin-degrading activity of intact and subcellular components of human fibroblasts

We have studied insulin degrading activity (IDA) in cultured human fibroblasts and assessed the effect of various inhibitors of insulin processing on IDA. To evaluate the role of three enzymes of insulin degradation (neutral protease, microsomal glutathione insulin transhydrogenase, and lysosomal acid protease), we subfractionated homogenized fibroblasts into membrane (and nuclei) cytosol, mitochondria, microsomes, and lysosomes. Greater than 90% of IDA was found to be present in the cytosolar fraction containing neutral protease. IDA in intact fibroblasts was completely inhibited by 1 mM N-ethylmaleimide and partially by 0.5 mM dansylcadaverine (75%), 0.5 mM chloroquine (48%), 1 mg/ml bacitracin (32%) and Trasylol (30%). Lidocaine (5 mM) and glucagon (10(-6)M) exhibited about 15% inhibition with minimal inhibition (7%) by nonsuppressible insulin-like activity. Study of similar inhibitors on subfractionated components indicated inhibition of cytosolar enzyme by N-ethylmaleimide (100%), glucagon (30%), chloroquine (41%), nonsuppressible insulin-like activity (30%), Lidocaine (25%), dansylcadaverine (16%), and bacitracin (11%). Incubation of ammonium sulfate-fractionated cytosolar enzyme at 37 C with A14-125I-insulin resulted in generation of two intermediate peaks as early as 1 min. These peaks could be identified by HPLC but not by molecular sieve chromatography. These intermediates exhibited less immunoprecipitability with antiinsulin antibody and receptor binding with liver membrane preparations than intact insulin. Further incubation of A14-125I-insulin with the cytosolar enzyme(s) resulted in reduction of these peaks as well as insulin and formation of 125Iodotyrosine peak. We conclude that human fibroblast is capable of metabolizing cell-associated A14-125I-insulin in a time- and temperature-dependent manner. This process is inhibited by various inhibitors of insulin processing. The bulk of IDA consists of soluble neutral protease(s) with properties similar to other more purified neutral insulin protease preparations. This fraction, similar to the intact fibroblast degrades insulin to two intermediates with similar molecular weight to that of intact insulin but with more hydrophilicity and less binding affinity to antiinsulin antibody and liver membrane than intact insulin.