Biologic activities of biosynthetic human insulin in healthy volunteers and insulin-dependent diabetic patients monitored by the artificial endocrine pancreas

[Diabetes mellitus in Anaesthesia - Optimal Blood Sugar Control in the Perioperative Phase]

Uncontrolled high blood sugar can be dangerous for diabetics throughout the perioperative period - in particular, when blood glucose levels exceed a threshold of 250 mg/dl or HbA_1c levels are higher than 8.5 - 9%. In such cases, all elective surgery should be withheld to minimize the risk of severe complications. Due to their cardiovascular comorbidities, diabetics are commonly overrepresented in hospitals, tend to require inpatient care for an extended period of time, and suffer from higher mortality rates. In order to reduce negative outcomes, blood glucose levels should be targeted to 140 - 180 mg/dl on intensive care units or during surgery. Current literature suggests that non-critically ill diabetics should be treated with rapid-acting insulin analogues subcutaneously in operating theatres, whereas critically ill patients should receive continuous intravenous insulin infusions using a standardized protocol. In summary, this review can give a hand in dealing with diabetics during the perioperative period and offers guidance in controlling blood sugar levels with the help of oral antidiabetic drugs and insulin.

Postprandial hyperglycaemia in type 2 diabetes: pathophysiological aspects, teleological notions and flags for clinical practice

Type 2 diabetes subjects carry an excess risk for micro- and macrovascular disease and a higher cardiovascular morbidity and mortality rate. The beneficial impact of tight glycaemic control-evidenced by the integrated marker of fasting glucose and postprandial glucose values, the HbA1c-for the prevention of microvascular complications is definitely confirmed. Over the past few years, several studies have identified postprandial hyperglycaemia as a better predictor of cardiovascular or even of all-cause mortality, as well as an independent risk factor for atherosclerosis. The continuous glucose monitoring could offer a rationale means for the detection of postprandial hyperglycaemia and ultimately for its effective management. Advances in technology keep a promise for a reliable, convenient and closer to the idea of the artificial endocrine pancreas glucose sensor. Subcutaneous glucose levels charted by one of the new sensors were found to be well correlated with venous glucose measurements. Intervention for a healthy lifestyle is frequently hampered by patients' poor compliance. The availability of diverse antidiabetic agents provides options for targeting the glycaemic goal and a choice more fitted to the particularized pathophysiology of each individual subject. Drugs targeting postprandial glycaemia may prove to represent the 'sine qua non' for the 'return' of postprandial glucose values at a 'non-deleterious' threshold, either as monotherapy for the early stages of the disease or as combination therapy later in the progression of diabetes.

Physiological responses during hypoglycaemia induced by regular human insulin or a novel human analogue, insulin glargine

AIM

Glargine, a product of recombinant technology, has different structural and physicochemical properties compared with native human insulin. We determined whether such differences are associated with alterations in the responses to hypoglycaemia induced by glargine.

METHODS

Nineteen adults (six healthy and 13 with type 1 diabetes) underwent a 5-h hyperinsulinaemic (2 mU/kg/min(-1)) stepped hypoglycaemic clamps (hourly targets of 4.7, 4.2, 3.6, 3.1 and 2.5 mmol/l, respectively) on two occasions using intravenous infusion of regular human insulin or glargine, in random sequence. Hypoglycaemic symptoms, counter-regulatory hormones and glucose disposal rates were assessed at intervals throughout the clamps. A 1-week 'wash out' period was observed between studies.

RESULTS

The peak total symptoms scores (mean +/- s.e.m.) at nadir blood glucose (2.5 mmol/1) were 18.83 +/- 2.68 (healthy) and 17.46 +/- 3.62 (diabetic) during regular insulin, and 18.50 +/- 3.20 (healthy) and 19.08 +/- 3.83 (diabetic) during glargine infusion. The peak epinephrine levels during hypoglycaemia were 767.8 +/- 140.4 pg/ml (regular insulin) and 608.8 +/- 129.9 pg/ml (glargine) among healthy subjects, and 332.5 +/- 54.8 pg/ml (regular insulin) and 321.8 +/- 67.4 pg/ml (glargine) in diabetic patients. Diabetic patients had blunted glucagon responses during hypoglycaemia with either insulin. Both insulins also elicited similar rates of glucose disposal.

CONCLUSIONS

We conclude that insulin glargine and regular human insulin elicit comparable symptomatic and counter-regulatory hormonal responses during hypoglycaemia in healthy or diabetic subjects, and induce similar rates of glucose disposal. Since glargine is designed for subcutaneous (s.c.) use, it is possible (though unlikely) that our findings obtained using an intravenous protocol could differ from responses to hypoglycaemia induced by the s.c. route.

Human insulin and hypoglycaemia: a literature survey

Thirty-nine clinical studies and 12 epidemiological reports comparing human insulin and porcine insulin were reviewed. Twenty-five studies (encompassing 338 subjects) showed identical symptoms and physiological response to acute hypoglycaemia overall. Fifteen studies (encompassing more than 1253 patients) showed identical incidence of hypoglycaemia overall and similar symptoms with the two types of insulin. Twelve studies showed identical incidence of hypoglycaemia overall with the two types of insulin. Thus, the overwhelming evidence from a large number of studies including a large number of patients suggests that: (1) human and porcine insulin do not provoke different hormonal responses to hypoglycaemia; (2) they do not cause different symptoms of hypoglycaemia; (3) the incidence of severe hypoglycaemia with human insulin does not differ from that of porcine insulin.

A comparative study on the hormonal responses to insulin-induced hypoglycaemia using semisynthetic human insulin and pork insulin in patients with type 1 diabetes mellitus

In order to enlighten the controversy on whether human and pork insulin result in different hormonal responses to insulin-induced hypoglycaemia, eight C-peptide negative, diabetic patients without measurable circulating insulin-binding antibodies were exposed to insulin-induced hypoglycaemia in random order with highly purified pork insulin (Actrapid) and semisynthetic human insulin (Actrapid Human). Hypoglycaemia was provoked by a constant rate IV infusion of insulin (0.034 U kg-1 h-1) for 3 h after which the blood glucose recovery was assessed for an additional period of 60 min. Both insulin preparations gave close to identical responses for glucose, glucagon, growth hormone, adrenaline, and somatostatin. The circulating noradrenaline levels were higher during the infusion of pork insulin which also yielded a more prominent response of pancreatic polypeptide and, after cessation of the insulin infusion, plasma cortisol was also higher following pork insulin. It is concluded that human and pork insulin induce close to identical responses of the important counter-regulatory hormones during hypoglycaemia in Type 1 diabetic patients.

24-h blood glucose pattern in type I and type II diabetics after oral treatment with pentoxifylline as assessed by artificial endocrine pancreas

Based on the known action of xanthine derivatives on the insulin secretion, the effect of pentoxifylline on carbohydrate homeostasis of type I (IDDM) and type II (NIDDM) diabetics was investigated. Pentoxifylline is known to exert a favorable influence on hemorheological disturbances in such patients. Twenty-four hour blood glucose pattern and insulin requirements were evaluated in type I and type II diabetics by the use of the artificial pancreas before and after a 14-day treatment with pentoxifylline 400 mg p.o. (Trental 400) t.i.d. During the stabilization period before treatment with pentoxifylline, NIDDM patients required 10.1 +/- 3.8 U of insulin and the IDDM 35 +/- 13.7 U. After 2 weeks on pentoxifylline, NIDDM required only 6.3 +/- 2.8 U (p less than 0.05) and IDDM 28.5 +/- 9.7 U (n.s.). Average blood glucose during the 24h decreased by 15.8 +/- 3.5% in NIDDM and by 10.3 +/- 2.5% in IDDM. Moreover, a significant smoothing of glucose fluctuations during the 24h was noted in both groups. It is concluded that pentoxifylline administered concurrently to any antidiabetic type of treatment leads to better blood glucose control as well as to prevention or delay of vascular complications.

A comparison of semisynthetic human NPH insulin and porcine NPH insulin in the treatment of insulin-dependent diabetes mellitus

Twenty-two insulin-dependent diabetic patients participated in a double-blind, cross-over study, where treatment with semisynthetic human NPH insulin (Novo Industri) was compared with porcine NPH insulin (Nordisk). Each treatment period lasted 8 weeks. Blood glucose level, glycosylated haemoglobin, insulin requirements, and frequency of hypoglycaemic events were compared. No difference was found in 24-hour blood glucose profiles. Fasting blood glucose level was 8.3 mmol/l during treatment with human insulin and 8.7 mmol/l during treatment with porcine insulin (p less than 0.1). Mean HbA1c was 7.7% at the end of study compared to 9.5% at baseline (p less than 0.01), but this decline in HbA1c was independent of the treatment regimen. Forty-six hypoglycaemic events occurred during treatment with human insulin compared to 39 events during treatment with porcine insulin. No difference was found regarding insulin requirements during the study. It is concluded that semisynthetic human NPH insulin is indistinguishable from porcine NPH insulin with respect to 24-hour blood glucose profile, HbA1c level and insulin dose requirements.

A double-blind study of the efficacy of neutral human and porcine insulin in type I diabetes using a glucose-controlled insulin infusion system

The comparative potency of equimolar amounts of soluble porcine and semisynthetic human insulin were studied in ten patients with type 1 diabetes in acute experimental situations. In both situations residual subcutaneous insulin depots were eliminated by intramuscular treatment exclusively with soluble insulin four days before the experiments. Then, practically identical metabolic states were achieved by connecting the patients to a glucose-controlled insulin infusion system (Biostator) 12 hours before the study. In one study, 0.5 g/kg body weight of glucose was administered intravenously as a bolus, and thereafter insulin was infused at a rate of 1.0 mU/kg/min. The decline in blood glucose was rectilinear and identical for the two insulins: y = -1.18x + 206 and y = -1.17x + 205. The insulin effect is well below maximum, and a 10% increase in the infusion rate of insulin was easily detected. Although changes in blood glucose and pancreatic glucagon were identical, a significantly lower plasma growth hormone level was noted after human insulin infusion. In the second study, 24 hours of near-normoglycemia was attained by the glucose-controlled insulin infusion system, the patients being supine and having identical meals at identical intervals. The diurnal blood glucose, plasma growth hormone, and pancreatic glucagon patterns were identical and the total 24 hour insulin consumption was 47.7 +/- 3.5 units and 47.7 +/- 3.7 units for the two insulins.

Human (recombinant DNA) and porcine NPH insulins are unequally effective in diabetic patients. A comparative study using continuous blood glucose monitoring

The hypoglycemic activities of NPH biosynthetic human and pork insulins were compared in eight insulin-dependent diabetic patients using continuous blood glucose monitoring. After an overnight normalization of blood glucose levels, either human or pork NPH were injected subcutaneously in random order. Blood glucose was continuously recorded during 9.5 h while patients were consuming their usual diet. After NPH biosynthetic human insulin, blood glucose levels from the 2nd to the 9th h post-injection were lower as well as the glycemic nadir. The area under the curve was smaller after human than after pork insulin. But, in the last half-hour of the experiment, blood glucose was falling after pork insulin, while it was rising after human insulin. Under the conditions of this study, our results demonstrate that NPH biosynthetic human insulin may be more effective than NPH pork insulin, due to more rapid subcutaneous absorption but its duration is shorter than after porcine NPH insulin. These data may be of importance in the treatment of insulin-dependent diabetes mellitus.

Comparison of porcine and semisynthetic human insulins using euglycemic clamp-derived glucose-insulin dose-response curves in insulin-dependent diabetes

In order to compare the biologic effectiveness of porcine and semisynthetic human insulins, a euglycemic clamp method was used in eight insulin-dependent diabetic subjects. Each subject was tested for each insulin on separate days. In order to derive glucose-insulin dose-response curves for both insulins, sequential but constant infusion rates of 0.2, 0.5, 1.0, and 2.0 mU/kg/min were performed. Plasma glucose levels attained during the euglycemic clamp were 96 +/- 3 mg/dL. At each insulin infusion rate, the steady-state glucose infusion rate required to maintain euglycemia was measured. At each increment of insulin infused, steady-state glucose infusion rates for porcine insulin were 1.12 +/- 0.22, 1.90 +/- 0.59, 4.28 +/- 0.61, and 9.37 +/- 0.66 mg/kg/min compared with 1.27 +/- 0.42, 2.38 +/- 0.20, 4.25 +/- 0.43, and 8.87 +/- 0.67 mg/kg/min for semisynthetic human insulin. By ANOVA, no significant difference was noted between the two insulins. Because insulin infusion rates may not result in predictable circulating free insulin levels in subjects who have circulating insulin antibodies, free insulin levels were determined. When steady-state glucose infusion rates were compared with free insulin levels achieved at the four insulin infusion rates, dose-response curves for both porcine and semisynthetic human insulins were virtually identical. These data suggest that semisynthetic human insulin has equivalent biologic effects on overall glucose metabolism compared with porcine insulin in insulin-dependent diabetes.

Human insulin--medical progress?

Human insulin is now produced in commercial scale by semisynthesis from porcine insulin or by recombinant DNA techniques. Comparative studies in non-diabetic or diabetic subjects on the hypoglycaemic effect of human insulin after intravenous or subcutaneous administration do not indicate that human insulin has advantage over highly purified pork insulin. In two of the three studies in which plasma insulin levels were examined after subcutaneous injection the results suggest that absorption of biosynthetic human insulin may be more rapid than that of purified porcine insulin. The amount of insulin needed to maintain normoglycemia in subjects with insulin-dependent diabetes, studied with a glucose controlled insulin infusion system was generally the same with human and pork insulin. Studies concerning subcutaneous absorption of NPH insulin in patients with insulin-dependent diabetes are needed. Long-term studies on the tendency of human insulin to induce antibody production are still lacking. Scientifically, the production of human insulin by recombinant DNA methods is a great advance. It remains, however, to be shown that human insulin has any clinical advantages over porcine insulin.

Insulin pharmacokinetics following continuous infusion and bolus injection of regular porcine and human insulin in healthy man

To determine the pharmacokinetics of insulin administered by intravenous (IV) and subcutaneous (SC) pump treatment as well as by the conventional subcutaneous route, six insulin preparations of either porcine or human amino acid sequence were investigated intraindividually following IV or SC insulin infusion at two different rates (Study I) and three preparations were investigated after SC bolus injection (Study II) in healthy men. Insulin release was suppressed in Study I by IV administration of somatostatin (500 micrograms/hr) to avoid interference by endogenous insulin with the measurement of exogenous insulin. Hypoglycemia was prevented by IV administration of glucose. The data obtained demonstrated (1) greater serum concentrations of immunoreactive insulin (IRI) during continuous IV insulin infusion (141 +/- 10 (SEM) pmole/liter) than during SC insulin infusion (54 +/- 3 pmole/liter; P less than 0.0005) (0.8 U/hr); (2) return of serum IRI to baseline values following a 17-minute square wave insulin infusion (12.8 U/hr; time: 0 to 17 minutes) within 40 minutes after IV insulin infusion but not before 180 minutes after the end of SC insulin infusion; (3) peak serum IRI at 60 to 90 minutes after conventional SC insulin injection returning to baseline values at 300 minutes; and (4) identity of the pharmacokinetics of pumped human and porcine insulin within a given group as well as of the accompanying metabolic dynamics of blood glucose and nonesterified fatty acids, but heterogeneity of serum insulin after its SC bolus injection. We conclude that (1) the pharmacokinetic behavior of regular insulin depends primarily on its route of administration; (2) continuous IV infusion of an insulin dose causes significantly higher serum insulin levels than the SC administration of the identical insulin dose, and (3) hyperinsulinemia caused by a square wave insulin infusion (12.8 U/hr; time: 0 to 17 minutes) requires more than four times longer to return to baseline levels following SC administration than after IV administration of the insulin. These differences in the pharmacokinetic behavior of insulin cause a reduced bioavailability of SC administered insulin and have to be taken into account when instituting insulin treatment by various routes.

The new insulins. Their characteristics and clinical indications

In the past 10 years the techniques of gel filtration and ion exchange chromatography have made available insulins of markedly enhanced purity. These highly purified insulins have made immunological insulin resistance a rarity, and result in absent or clinically insignificant levels of insulin antibodies in insulin-treated diabetics. Insulin allergy has not been reported with highly purified insulins alone, and is rare even when the patient has previously received recrystallised insulin. Generalised allergic reactions to insulin and insulin resistance are associated with the enhanced immunological reaction to intermittent insulin therapy. The use of highly purified insulins for short courses of treatment is therefore mandatory, particularly in patients with infections. Injection-site lipoatrophy, a relatively common occurrence with the older insulins, disappears on changing to highly purified preparations. Following a change to highly purified insulins, insulin dose requirements will fall gradually with insulin antibody levels. When switching from conventional beef to highly purified pork insulins, a more immediate change in dose requirements may occur so that prospective reductions in insulin dose are indicated. It is still uncertain whether moderate levels of insulin antibodies are associated with any difference in metabolic control. This is partly a reflection of difficulties in measuring diabetic control, and partly a lack of properly designed studies. Current insulins of both older and newer types give plasma insulin profiles that are far from physiological. Insulin antibodies cross the placenta and may contribute to increased fetal insulin secretion and neonatal hypoglycaemia. Pre-pregnant patients should be changed to the newer preparations. Highly purified insulins cost little more than conventional insulins in the free market, and should be used in all newly diagnosed insulin-requiring diabetics. More recently, human insulin has become available through both DNA recombinant technology and amino acid substitution techniques. It has proved to have identical characteristics to pork insulin both in vitro and in normal subjects. Clinical trials with human insulin are at present in progress.