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Effects of Timing of Administration and Meal Composition on the Pharmacokinetic and Pharmacodynamic Characteristics of the Short-Acting Oral Hypoglycemic Agent Nateglinide in Healthy Subjects

Diabetes Research Unit (S.D.L., D.R.O.), Llandough Hospital, Penarth, South Glam, CF64 2XX; and Ajinomoto Pharmaceuticals Europe Ltd. (D.M.A.), Redhill, Surrey RH1 1RX, United Kingdom

Address all correspondence and requests for reprints to: Dr. S. D. Luzio, Diabetes Research Unit, Llandough Hospital, Penlan Road, Penarth, South Glam, CF64 2XX, United Kingdom. E-mail: luzio{at}cf.ac.uk

Abstract

These studies examined the influence of timing of administration of nateglinide on the glucose profile and ß-cell secretory response to a standardized test meal and the effect of meal composition on the pharmacokinetic and pharmacodynamic profile. In study 1, nateglinide (60 mg) or placebo was given orally at -10, -1, or +10 min to healthy subjects (n = 12), in relation to a standardized test meal (500 kcal) that commenced at 0 min. In study 2, also in healthy subjects (n = 12), a single oral dose (60 mg) of nateglinide was given either 10 min before or 10 min after the start of each of three different test meals (i.e. high in carbohydrate, fat, or protein). In both studies, the postmeal observation period was a minimum of 240 min. In the first study premeal (-10,-1 min), administration of nateglinide led to earlier and higher peak plasma nateglinide concentrations, compared with postprandial dosing (+10 min). A significantly lower maximum postprandial glucose concentration was seen with preprandial dosing compared with either placebo (P < 0.01) or nateglinide given postprandially (P < 0.01). The impact on the glucose profile was consistent with the enhanced insulin profiles after nateglinide, resulting in higher peak plasma insulin concentrations compared with placebo (P < 0.01). Study 2 confirmed the greater impact of pre- vs. postprandial dosing on the glucose and insulin profiles, irrespective of meal type. Nateglinide administration, before a meal, resulted in a more rapid rise and higher peak nateglinide plasma concentrations, irrespective of meal composition. Preprandial administration of nateglinide was more effective in reducing prandial glucose excursions, compared with postmeal dosing (+10 min), a consequence of the earlier insulin response.

TYPE 2 DIABETES mellitus is a heterogeneous disorder characterized by both peripheral insulin resistance and abnormal insulin secretion, although there is continuing controversy as to the primary lesion (1, 2, 3). Insulin secretion in type 2 diabetes is characterized by a loss of the first-phase insulin response to iv glucose, with delayed and inadequate second phase of insulin secretion, in the face of elevated circulating glucose levels (4, 5). Despite the lack of first-phase insulin secretion to iv glucose, the response to amino acids is preserved (6). This observation has formed the basis for the development of nateglinide, a phenylalanine derivative with potent in vivo and in vitro ß-cell secretagogue activity.

Nateglinide (N-[trans-4-isopropylcyclohexylcarbonyl]-D-phenylalanine) is a novel amino acid derivative of cyclohexane and phenylalanine. It is not chemically related to the sulfonylurea compounds but has been shown to similarly stimulate insulin release from the pancreatic ß-cell via closure of ATP-sensitive K⁺ channels, depolarization, and gating of the voltage-sensitive Ca²⁺ channels (7, 8). Nateglinide has been shown to bind to sulfonylurea receptors on the ß-cell membrane and be more effective than sulfonylureas in increasing Ca²⁺ concentration in ß-cells during metabolic inhibition (9). Glucose-stimulated perfusion studies in the rat pancreas suggest that nateglinide does not independently stimulate insulin secretion but potentiates its early release only in the presence of glucose (10). Neither has it an independent action on insulin exocytosis, only via its action on the ATP-sensitive K⁺ channel (11). Nateglinide is absorbed in the small intestine and is metabolized mainly in the liver, with approximately two thirds excreted in the feces and about one third in the urine (12). In vitro and in vivo studies have demonstrated that nateglinide stimulates insulin secretion, with a rapid onset and short duration of action. Its potential, therefore, is to reduce prandial blood glucose levels, with little risk of interprandial hypoglycemia (12, 13). Nateglinide has a synergistic effect with postprandial glycemia to stimulate early-phase insulin secretion (9, 14), which is of importance in patients with type 2 diabetes (15). Replacement of the early-phase insulin secretion by infusion of insulin has been shown to improve postprandial glycemia and reduce postprandial hyperinsulinemia (16, 17, 18).

The objective of our studies was to determine the potential influence of pre- and postprandial timing of administration of a single oral dose of nateglinide, in relation to a standardized test meal (study 1), and to examine the effect of meal composition on its pharmacokinetic and pharmacodynamic characteristics (study 2).

Subjects and Methods

Experimental subjects

The studies were carried out in two separate groups of healthy male subjects, with the two study protocols approved by the Local Research Ethics Committee. All subjects gave written informed consent before the study. Before and after the study, all subjects underwent a full health screen.

Materials and methods

Study 1: Effect of meal related timing of administration. This was a double-blind, placebo-controlled, randomized four-way cross-over designed study with a washout period of at least 7 d between the individual study days. All treatment allocations (three active and one placebo) were balanced by full randomization using three replicates of a 4 x 4 Latin square.

Subjects (n = 12) were studied on 4 separate study days. After a 12-h overnight fast, three basal blood samples were taken (-30, -10, and 0 min). At time 0 min, the subjects were given a 500-kcal standardized meal (Table 1, high carbohydrate), which was consumed within 10 min. Active drug (60 mg) or placebo was given at -10, -1, or +10 min in random order. To preserve the blindness of the study, an identical placebo tablet was given at the other two time points. Frequent blood samples were then taken over the following 4 h.

Study 2: Effect of meal type and timing of administration. This study was a randomized six-way cross-over study in which a single dose of nateglinide was given at two different times (-10 and +10 min) in relationship to three different test meals (a high-carbohydrate, high-fat, or high-protein meal, all approximately 500 kcal) (Table 1). Each treatment was separated by a washout period of at least 1 wk. Because it was impossible to disguise the differences between the various meals, the order of administration of the three different test meals was randomized. The nateglinide doses remained blinded. All subjects received each of the three meals, each in association with the two different nateglinide administration times.

Each subject (n = 12) underwent 6 separate study days, after a 12-h overnight fast. Two basal blood samples were taken (-10 and 0 min); and at time 0 min, the subjects were given one of the test meals, which was consumed within 10 min. On each study day, subjects were given both active drug (60 mg nateglinide) or placebo, both -10 or + 10 min after the commencement of the test meals, in random order. Further blood samples were taken over the following 310 min.

The subjects were 30.1 ± 8.0 yr old (mean ± SD; range, 20–42 yr) and their body mass index was 24.9 ± 2.4 (range, 21.8–28.7) kg/m².

Assays. Blood samples were taken for assay of plasma glucose (Yellow Springs Analyser 2300; YSI, Inc., Yellow Springs, OH), insulin (K6219, DAKO Diagnostics, Ely, Cambs, UK), C-peptide (K6218, DAKO Diagnostics), and nateglinide concentrations. The cross-reactivity of proinsulin in the insulin assay was less than 2%. The C-peptide assay cross-reacted less than 2% with insulin and approximately 100% with proinsulin. Nateglinide was assayed using a specific fully validated HPLC method.

Statistical methods. Results are given as mean ± SD. The area under the plasma concentration time curve [area under the curve (AUC)] was calculated using the trapezoidal rule. For nateglinide, maximum concentration (C_max) was the maximum observed concentration, and maximum time (T_max) was the time to C_max in the period after drug administration. For the pharmacodynamic indices (glucose, insulin, and C-peptide) C_max and T_max were measured from the start of the meal. Statistical analysis was carried out by means of ANOVA. A P-value of less than 0.05 was considered to be significant.

Results

Study 1: Effect of meal related timing of administration

The mean plasma glucose, insulin, C-peptide, and nateglinide responses are shown in Fig. 1. Compared with placebo, a reduction in peak plasma glucose was observed when nateglinide was administered at -10 (P < 0.01) and -1 min (P = NS), which was consistent with a more rapid rise in plasma insulin when nateglinide was given at these earlier times. In contrast, nateglinide administration at +10 min had no influence on the peak postprandial glucose level but resulted in a delayed hypoglycemic response when compared with placebo. This reflected the delayed insulin response, reaching a peak level at 44 min, compared with administration at -10 min, which reached a peak at 30 min.

View larger version (18K): [in this window] [in a new window]   Figure 1. Mean plasma glucose, insulin, C-peptide, and nateglinide levels in healthy subjects (n = 12) after administration of 60 mg nateglinide at either -10 (—), -1 (—), or +10 min (•—•) or placebo (x—x), in relation to a 500-kcal standardized meal.

For C-peptide, timing of administration of nateglinide did not significantly affect the mean C_max. Treatment given before the meal gave significantly shorter T_max (both P < 0.05) than when given 10 min after the start of the meal; however, there was no significant difference between any nateglinide treatment and placebo. Timing of administration of nateglinide made little difference to the overall AUC_0–240.

Details of C_max, T_max, and AUC_0–180 for plasma nateglinide concentrations are summarized in Table 2. Administration of nateglinide at -10 min achieved earlier and higher (but not statistically significant) plasma nateglinide concentrations, compared with administration at +10 min, which resulted in a marked delay in absorption. For AUC_0–180, the drug timing showed no significant effect (P = 0.12); but as expected, the mean time to peak concentration increased with later administration of the drug. The mean T_max was significantly shorter (P = 0.02) when the drug was given 10 min before the meal than when it was given 10 min after the start of the meal. Administration of nateglinide at -1 min led to an intermediate response.

The comparison of adjusted glucose AUC_0–60 change, from baseline, with adjusted insulin T_max (adjusted for subject and period effects) is shown in Fig. 2. There was a statistically significant difference (P < 0.01) among all treatments.

View larger version (19K): [in this window] [in a new window]   Figure 2. Adjusted glucose AUC0–60 change from baseline vs. adjusted insulin Tmax (adjusted for subject and period effects).

Details of the different meal compositions and dose timing effects on AUC_0–300, C_max, and T_max are included in Table 3. The mean plasma glucose, insulin, and nateglinide responses are illustrated in Fig. 3.

View larger version (27K): [in this window] [in a new window]   Figure 3. Mean plasma glucose, insulin, and nateglinide concentrations in healthy subjects (n = 12) after administration of 60 mg nateglinide at -10 (—) or +10 (–) min in conjunction with a high carbohydrate, high fat, or high protein meal.

Premeal, compared with postmeal administration of nateglinide, led to a reduced early (30–60 min) postprandial plasma glucose excursion with all three types of meals (high-carbohydrate, high-fat, and high-protein). Glucose excursions (AUC_0–300) were similar after the high-fat and high-protein meals, both significantly lower than that observed after the high-carbohydrate meal (P < 0.01). These alterations in plasma glucose concentrations were consistent with a more rapid insulin response after premeal (compared with postmeal) administration of nateglinide. Mean AUC_0–300 plasma insulin concentration was significantly lower after the high-fat meal (P = 0.001), and the timing of administration of nateglinide made little difference to the AUC_0–300. For all meal types, the mean insulin T_max was significantly longer when the study drug was given after the meal (P < 0.05).

The postprandial C-peptide response generally reflected the postprandial insulin profiles (Table 3). The high-carbohydrate meal gave a significantly higher mean AUC_0–300 for C-peptide than the high-protein meal (P < 0.05), which itself had a higher mean AUC_0–300 than the high-fat meal (P < 0.01). The time to C_max was delayed when nateglinide was given postprandially (P = 0.001) and also was significantly lower after the high-fat meal than the other meal types (P < 0.05).

In both studies, nateglinide was well tolerated, and no serious adverse events were reported.

Discussion

The knowledge that the early-phase insulin response in type 2 diabetic patients is better retained to iv amino acids, compared with glucose, led to the development of nateglinide, a phenylalanine derivative with ß-cell secretagogue activity. The studies reported have examined the potential influence of pre- and postprandial timing of administration of a single (60 mg) oral dose of nateglinide, in relation to a standardized test meal and also the effects of meal composition on its pharmacokinetic and pharmacodynamic characteristics.

In a first study, administration of nateglinide before the meal (either -10 or -1 min) demonstrated a significant benefit in reducing peak postprandial plasma glucose concentrations, compared with placebo, by inducing a more rapid increase in insulin concentrations in response to the meal. In contrast, administration of nateglinide, 10 min after the commencement of the test meal, had little or no impact on reducing postprandial glucose excursions. However, a higher and delayed peak insulin concentration was observed with nateglinide given 10 min after food, compared with placebo, resulting in a delayed hypoglycemic response. Administration of nateglinide at -10 min preprandially led to a more rapid rise in plasma nateglinide concentrations, whereas administration 10 min after the start of the meal led to a much reduced and delayed rise in plasma concentrations. This study, therefore, demonstrates that nateglinide should be administered before a meal to achieve a more rapid insulin secretory response, with the benefit of greater reduction in peak postprandial glucose levels. This was also confirmed by the statistically significant correlation (P < 0.01 for all treatments) of glucose AUC_0–60 with insulin T_max, an earlier insulin peak resulting in a reduced glucose excursion. In a study in monkeys, Dunning and Paladini (19) showed that administration of nateglinide, before food, leads to an increase in insulin secretion before the insulin response from ingestion of the meal. In this study in nondiabetic humans, this could not be confirmed; and no increase in insulin levels, after administration of nateglinide at -10 min, and in the basal sample before consumption of the meal, could be observed.

In a second study, both timing of administration (-10 and +10 min) and meal composition (high-carbohydrate, high-fat, high-protein) were examined. Nateglinide administration before the meal consistently led to a more rapid rise, with higher peak in plasma concentrations, than when administered postprandially. The premeal administration resulted in a greater reduction in postprandial glucose excursions with all meal types. As expected, the high-carbohydrate meal resulted in higher peak plasma glucose concentrations, compared with the high-fat and high-protein meal types, with the mean plasma insulin AUC during the high-fat meal being significantly lower than during either the high-carbohydrate or high-protein meals.

Meal composition had no effect on the plasma nateglinide profile, which is of particular importance because nateglinide is a D-amino acid derivative, and thus there was the possibility that its absorption could be influenced by the presence of high amino acid concentrations. The findings in this study clearly demonstrate that, even in the presence of a high-protein meal (32% calorific value derived from protein), no effect on absorption of nateglinide was observed.

Plasma insulin concentration, in response to a mixed meal in nondiabetic subjects, reaches peak concentrations within an hour before returning to fasting levels within 2–3 h. In contrast, in type 2 diabetic subjects, the response is slower, with delayed peak concentration 2–3 h after commencement of a meal. Evidence supports the fact that all type 2 diabetic subjects during the early postprandial phase are relatively insulinopenic, compared with age- and weight-matched healthy subjects (5, 20, 21). Consequently raised postprandial glucose concentrations are largely the result of the loss of early-phase insulin secretion in type 2 diabetic patients; and it has been shown that replacement of the early-phase insulin response with an iv infusion of insulin results in reduced postprandial hyperglycemia and hyperinsulinemia (16, 17). A recent study, using the short-acting insulin analog lispro (18), has also confirmed the importance of restoring the early rise in plasma insulin in type 2 diabetic patients. In this study, using labeled glucose, it was shown that the early rise in insulin was associated with improved postprandial glucose tolerance attributable to a prompt and short-lived suppression of endogenous glucose production. The long-term consequences of postprandial hyperglycemia are related to increased cardiovascular risk (22, 23), possibly attributable to effects on oxidative stress and homeostasis in both nondiabetic and diabetic subjects (24). It has also been shown that lowering of the 2-h postprandial glucose concentration is more important than fasting plasma glucose for reducing cardiovascular risk (25). In study 2, glucose C_max was always lower when nateglinide was given before the meal, although glucose AUC_0–300 was consistently higher. Nateglinide may therefore play an important role in reducing the risk of cardiovascular complications by blunting the peak postprandial glucose concentrations.

To date, current treatments to restore insulin secretion in type 2 diabetes have largely been restricted to the use of the sulfonylurea group of insulin secretagogues. Most of these agents fail to restore early insulin secretion, only increasing the late phase of insulin secretion with the associated risk of hypoglycemia (26). The importance of early insulin secretion to the postprandial state has been recognized, and a number of nonsulfonylurea agents are available (12, 13, 27). Nateglinide, a phenylalanine derivative, is one of these agents; and in the studies described here, it has been shown that nateglinide potentiates the early insulin response to a mixed meal in healthy subjects. A significant interaction with food was observed, with the optimum time of administration being 10 min preprandial. In all subjects, nateglinide was well tolerated, and the few adverse events reported were not thought to be related to the trial medication.

In summary, irrespective of the type of meal, nateglinide given orally before food was more effective in reducing peak postprandial glucose excursions, compared with postmeal administration (+10 min), because of a significantly lower bioavailability of nateglinide during the early postprandial period. The time of administration of nateglinide is crucial in regulating postprandial glucose homeostasis. The results also support the premise that the early availability of insulin in response to a nutrient load is more important than the overall prandial insulin response. However, extrapolation of the results to type 2 diabetic patients should be made with caution until similar effects on early insulin response have been demonstrated in type 2 diabetic patients with defective ß-cell function.

Acknowledgments

Footnotes

Abbreviations: AUC, Area under the curve; C_max, maximum concentration; T_max, maximum time.

Accepted June 4, 2001.

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