Diabetologia 9 Springer-Verlag 1989

Transcription

1 Diabetlgia (1989) 32:28-33 Diabetlgia 9 Springer-Verlag 1989 Determinatin and kinetic analysis f nn-insulin mediated glucse uptake in Type 1 (insulin-dependent) diabetes mellitus S. L. Shumak, M. Gulan, B. Zinman and I. S. Gttesman Department f Medicine, University f Trnt, Trnt, Ontari, Canada Summary. In man, ttal glucse uptake is the sum f insulin mediated glucse uptake and nn-insulin mediated glucse uptake. The latter pathway has nt been examined in Type 1 (insulin-dependent) diabetes mellitus. In rder t assess nninsulin mediated glucse uptake in Type 1 diabetes, we measured steady-state rates f glucse uptake during glucse clamps at 5.27, 9.71 and 12.5 mml/1 using lw (.25 mu. kg- 1. rain- 1), intermediate (.75 mu. kg- 1. rain- 1) and high (1.5 mu.kg -1.min -1) insulin infusin rates in 1 subjects with Type 1 diabetes. Fr insulin infusin rates f.25,.75 and 1.5 mu. kg-1. rain-1 as plasma glucse rse frm 5.27 t 9.71 retl/l, ttal glucse uptake increased by 35, 43 and 52 percent respectively (p <.5 fr each insulin infusin rate). Fr all three insulin infusin rates, there was n significant increase in ttal glucse uptake as plasma glucse increased frm 9.71 t 12.5 mml/1. At each glycaemic level, glucs e uptake crrelated significantly with plasma free insulin (r=.81, p<.1 at 5.71 retl/l; r=.84, p<.1 at 9.71 mml/1; r =.73, p <.2 at 12.5 mml/1). Linear regressin analysis t a pint crrespnding t plasma free insulin equalling zer, yielded values fr nn-insulin mediated glucse uptake (mml. kg -1. rain -1) f.11,.14,.18 at plasma glucse f 5.27, 9.7 and 12.5 mml/1 respectively. Thus, in- creasing plasma glucse cncentratins were assciated with increasing rates f nn-insulin mediated glucse uptake. Fr each insulin infusin rate used, the percent f ttal glucse uptake accunted fr by nn-insulin mediated glucse uptake remained independent f plasma glucse cncentratin, but decreased as insulin infusin ralte increased. During the insulin infusin at.25 mu.kg-l.min -1, this percentage ranged frm 83.7 t 91.4%. Analysis f glucse uptake data derived fr theretical plasma insulin levels f, 4, 8 and 16 ~U/ml yielded linear Eadie-Hfstee plts (r = -.83 t -.99), suggesting that insulin increased Vmax but did nt alter Km. Hence, in these subjects with Type 1 diabetes, glucse uptake, bth insulin mediated and nn-insulin mediated can be described by Michaelis-Menten kinetics. Cmparisn f values btained fr Vmax and Km in the present studies f Type 1 diabetes with thse btaiined frm nn-diabetic subjects indicates that nn-insulin dependent glucse uptake in Type 1 diabetes is quantitatively similar t that f nndiabetic subjects. Key wrds: Type 1 (insulin-dependent) diabetes, glucse uptake, nn-insulin mediated glucse uptake, glucse kinetics. In man, in viv glucse uptake is the sum f insulin mediated glucse uptake (IMGU) and nn-insulin mediated glucse uptake (NIMGU). IMGU ccurs nly in insulin sensitive tissues such as muscle and adipse tissue; whereas NIMGU can ccur in bth insulin sensitive and insulin insensitive tissues (e.g. central nervus system). In the past decade, there have been many investigatins f IMGU in man [1]. In cntrast, there have been very few investigatins f NIMGU de- spite the fact that nn-insulin mediated pathways can accunt fr apprximately 7-85% f ttal glucse uptake in the pst-absrptive state. This has been demnstrated in bth nn-diabetic and Type 2 (nn-insulindependent) diabetic individuals [2, 3]. The rate f NIMGU maybe a reflectin f the activity f the glucse transprt system [4]. Defects in this system culd cntribute t the impairment f insulin actin bserved in many insulin resistant states including

2 S. L. Shumak et al.: Determinatin and kinetic analysis 29 Table 1. Mean values fr plasma glucse and free insulin. G - plasma glucse (mml/l). FIRI - free plasma immunreacrive insulin (txu/ml) Insulin infusin rate (mu. kg- 1. m- 1) Target glucse (mml/1) G 5.18_ _+.2 FIRI 28. _ _ G 5.33_ _+.2 FIRI 5.7 _ G _+.14 FIRI 137 _ _ _ _ that reprted t be present in Type 1 (insulin-dependent) diabetes mellitus [5, 6]. We therefre sught t study this system in Type 1 diabetes in rder t determine whether the apparent abnrmality f insulin actin present in Type 1 diabetes is secndary t a defect in NIMGU. Subjects and methds Subjects Ten subjects with Type 1 diabetes were studied. Type 1 diabetes diagnsed by the criteria f the Natinal Diabetes Data Grup [7] and cnfirmed by the absence f C-peptide respnse t an ral meal challenge (Sustacal, Mead-Jhnsn C., Belleville, Ontari, Canada) (pst-challenge C-peptide<.3 pml/ml). Their mean age was 33.7 _+ 2.8 years and their duratin f diabetes was years. Subjects averaged 13 _+ 2% f their predicted ideal bdy weight accrding t estimates btained using the Metrplitan Life tables f Subjects used 42.8 f insulin per day ( units, kg - a. d- ~). Seven subjects tk twice daily insulin injectins, I thrice daily and 2 subjects tk ne injectin daily. N subject had clinically significant diabetic cmplicatins. The mean haemglbin Alc was % (nrmal range 3-6%). N attempt was made t alter the glycaemic cntrl in ur subjects prir t acceptance int this study. Prcedures Upn entry int the study, each subject was randmised t underg three glucse clamps at ne f three insulin infusin rates (.25,.75 r 1.5 mu.kg-l.min-l). In the text, these rates are designated as lw, intermediate and high respectively. Tw subjects vlunteered fr further clamps and were assigned randmly t ne f the remaining insulin infusin rates fr a series f three further clamp studies. Intermediate acting insulin was discntinued 72 h befre each clamp study, and replaced by thrice daily injectins f regular insulin until 12 h prir t each clamp. At that time, a cntinuus intravenus infusin f regular insulin (Iletin II, Eli Lilly C., Indianaplis, Ind., USA) was given t achieve euglycaemia vernight (plasma glucse 5-6 mml/1) accrding t a mdificatin f a previusly published prtcl [8]. This infusin was cntinued until the start f the clamp perid the next mrning and then discntinued. All studies began at 8. hurs with the subject in the pst-absrptive state. Female subjects underwent each study in the fllicular phase f their menstrual cycle. The purpse, nature and risks f the investigatin were fully explained t the participants and written infrmed cnsent was btained. The prtcl was apprved by the Human Studies Cmmittee f the University f Trnt. Glucse clamps Vlunteers underwent three glucse clamps, each f 4 h duratin, with target glycaemic levels f 5.27, 9.71 and 12.5 mml/1. Fr a given vlunteer, the same insulin infusin rate was used in all three clamps. Fr all subjects the rder f target glucse levels was selected randmly, and the interval between clamp studies ranged frm tw t fur weeks. Glucse clamping was perfrmed as previusly described [9]. At the start f the clamp, a primed (22 p~ci) cntinuus (.22 5xCi/min) infusin f 3-[3H] glucse (New England Nuclear, Bstn, Mass., USA) was begun. Cncurrently, infusins f Smatstatin (Sern, Randlph, Mass., USA) at 25 ~xg/h and regular prk insulin (Iletin II, Eli Lilly) at ne f.25,.75 r 1.5 mu.kg -1 -rain -1 were begun. A priming dse f insulin was given intravenusly ver 1 s (and calculated accrding t the frmula: insulin prime (mu)= distributin vlume (1 ml/kg x bdy weight in kg)x desired increment in plasma insulin xu/ml) x.1. A basal plasma insulin cncentratin f 1 ~tu/ml and an insulin distributin vlume f 1% bdy weight were assumed [1]. Simultaneus with these infusins, a fifty percent slutin f glucse was infused at a variable rate in rder t maintain the plasma glucse at a cnstant level (5.27, 9.71 r 12.5 mml/1). In rder t prevent hypkalaemia and hypphsphataemia, a carrier slutin f.9 percent NaC1 cntaining.13 meq/ml ptassium and.9 mml/l phsphate was administered intravenusly at 3 ml/h. Analytical methds All bld samples were drawn frm an arterialised (7 ~ C) hand vein [11]. Plasma glucse and urine glucse were measured using the glucse xidase methd (Glucse Analyser II, Beckman Instruments, Fullertn, Calif, USA). Bld fr determinatin f free insulin was drawn int tubes cntaining 1 U/ml aprtinin (Trasyll, Miles Labratries, Rexdale, Ont., Canada) and placed n ice. Samples were centrifuged with minimal delay and the supernatants frzen at -2~ until assayed. Fllwing plyethylene glycl extractin f the serum [12], free insulin was determined by radiimmunassay using a single antibdy charcal separatin methd ]13]. Bld fr glucse specific activity was drawn int tubes cntaining NaF-xalate and placed n ice. Fllwing centrifugarin, glucse specific activity in the supernatant was determined as previusly described [14]. Glucse uptake rates Glucse specific activity was determined n timed samples taken during the last 3 min f each glucse clamp. Glucse uptake was then determined istpically using the equatin,s f DeBd et al. [15]. These have been shwn t accurately reflect glucse kinetics ver a wide range f nn-steady-state cnditins [1,6, 17]. A pl fractin f.5 was assumed. Calculated glucse uptake rates were crrected fr urine glucse lsses.

3 3 S.L. Shumak et al.: Determinatin and kinetic analysis Table 2. Rates f ttal glucse uptake (Rd) and percent f Rd accunted fr by nn-insulin mediated glucse uptake (%NIMGU) at the target glucse levels used in this study Insulin infusin Rd (mml. kg- 1. m- 1) % NIMGU rate (mu. kg- 1. m- 1) _ _ _ Statistical analysis All calculatins were made n mean steady-state data cllected ver the last 3 min f each clamp. Least squares linear regressin analysis was perfrmed n the data btained during the 5.27, 9.71, 12.5 mml/1 clamps, respectively. Glucse uptake was cnsidered as the dependent variable and plasma free insulin level as the independent variable. Fr each glycaemic level, the 'y' intercept (i. e. free insulin = ) f the regressin line was taken t represent NIMGU at that level [2]. Using these regressin equatins, values f glucse uptake were derived fr theretical plasma free insulin levels f, 4, 8 and 16 l-tu/ml. Eadie-Hfstee analysis f the glucse uptake data at these insulin levels was then perfrmed. The percent f ttal glucse uptake attributable t NIMGU (%NIMGU) was defined as 1 x NIMGU/ttal glucse uptake. Statistical cmparisn f rates f glucse uptake at varius plasma glucse and plasma free insulin cncentratin were made using paired and unpaired Student's t-tests. Cmparisns f multiple means was made using ne way analysis f variance (F test). All data in the text, tables and figures is given as mean + SEM. Results --=E (5 v.77, Plasma glucse (retl/i) Fig. 1. The relatinship between glucse uptake and plasma glucse during insulin infusin rates f 1.5 (A),.75 (n) and.25 (9 mu- kg-l.min -1. *p <.5 vs. glucse uptake at 5.27 mml/1 fr same insulin infusin rate Target glycaemic level was reached after , _3.1 and min fr clamps with glucse gals f 5.27, 9.71, and 12.5 mml/1 respectively. Preclamp glucse was , and fr clamps with glucse gals f 5.27, 9.71 and 12.5 mml/1 respectively. The mean values fr plasma glucse and free insulin during the study are listed in Table 1. Fr each insulin infusin rate, the free plasma insulin levels attained were similar fr clamps with target glucse f 5.27, 9.71 and 12.5 mml/i (pns by F test). As well fr each target glycaemic level, the glucse cncentratins achieved during the clamps at the three insulin infusin rates were nt statistically different (pns by F test). At plasma glucse f 5.27, 9.71 and 12.5 mml/1 respectively, glucse uptake (mml-kg-t.min -1) was , and at the lw insulin infusin rate,.24+.3, and at the intermediate insulin infusin rate, and.43.4, and at the high insulin infusin rate (Table 2). Thus, increasing plasma glucse cncentratin frm 5.27 t 9.71 at the lw, intermediate and high insulin rates was assciated with increases in glucse uptake f 35, 43 and 52%, respectively (p <.5). Fr all insulin infusin rates used, the change in glucse uptake assciated with increasing plasma glucse frm 9.71 t 12.5 mml/1 was nt significant (Fig. 1). Figures 2 a, b and c depict: the relatinship between glucse uptake and plasma free insulin levels during clamps with target gtycaemic levels f 5.27, 9.71 and 12.5 mml/1, respectively. In each case, a significant crrelatin was bserved (r =.81, p <.1 ; r =.84, p <.1 ; r =.73, p <.2 fr plasma glucse 5.27, 9.71 and 12.5 mml. 1, respectively). Linear regressin analysis t free plasma insulin cncentratin equalling zer yielded values fr NIMGU f.11,.14 and.18 mml.kg-l.min -1 at plasma glucse equalling 5.27, 9.71 and 12.5 mml/1 respectively. Table 2 lists values fr ttal glucse uptake and %NIMGU fr the plasma free insulin and glucse levels achieved in this study. Fr a given insulin infusin rate, the %NIMGU was independent f plasma glucse cncentratin. Hwever, the %NIMBU decreased as insulin infusin rate increased. Results f Eadie-Hfstee analysis f the glucse uptake data are illustrated in Figure 3. Fr each insulin level analysed, a strng crrelatin was btained (r = -.83 t -.99). In this analysis, the 'y' intercept is

4 S. L. Shumak et al.: Deternfnatin and kinetic analysis ~'~= ~'~ ~E.33,22 -~'~.68 ~Q" '~.66 ~E -.11 I I t l I I I I I ,22 a Free immunreactive insulin (pu/ml) = , '= -~r: Glucse uptake/glucse (kg -1.I-l.min-l.lO 3) Fig.3. Eadie-Hfstee analysis f glucse uptake at free insulin f (H), 4 (O----O), 8 ( H ) and 16 (A A) ~xu/ml _ze, ~176 the Vmax and the negative slpe is Km. Hence, it can be seen that with the increasing insulin cncentratin the Vmax prgressively increased. Km was unchanged (7.8, 8.2, 8.1, 7.9 mml/1) at insulin cncentratin f, 4, 8, and 16 ~U/ml. I I I I I I I I I I I Free immunreactive insulin (pu/ml) Discussin 9 '~ _ZE / I 1 I I I I I I I I Free immunreactive insulin (pu/mo Fig.2. a The relatinship between glucse uptake and plasma free immunreactive insulin at a glucse cncentratin f 5.27 mml/l. The least mean squares linear regressin line is shwn (y= x, r =.81, p <.1). b The relatinship between glucse uptake and plasma free immunreactive insulin at a glucse cncentratin f 9.71 retl/1. The least mean squares linear regressin line is shwn (y = x, r =.84, p <.1). e The relatinship between glucse uptake and plasma free immunreactive insulin at a glucse cncentratin f 12.5 mml/1. The least mean squares linear regressin line is shwn (y= x, r =.73, p <.2) Glucse uptake by mammalian cells is thught t ccur via glucse transprters lcated in the cell membrane [18, 19]. In vitr studies have shwn that insulin causes translcatin f these glucse transprters frm a cytplasmic pl t the cell membrane [18]. Thus, in insulin sensitive tissues, insulin culd augment glucse uptake by prviding additinal glucse transprters. In viv data btained frm nn-diabetic subjects has demnstrated that glucse uptake fllws Michaelis-Menten kinetics, with insulin increasing the Vmax but nt changing the Km [2]. This finding has been interpreted as indicating that insulin increases the number f effective glucse transprters withut changing their affinity fr glucse [4, 2]. Glucse transprt ccurring independently f insulin actin may reflect the intrinsic activity f the glucse transprter system [4]. A defect in this intrinsic activity culd impair glucse uptake even after insulin has induced translcatin f cytplasmic transprters t the cell membrane. With many currently emplyed techniques fr assessing insulin resistance, such an impairment might be taken, incrrectly, t indicate a primary defect in insulin actin [1, 4]. In this investigatin, we studied NIMGU in subjects with Type 1 diabetes in rder t determine if the insulin resistance f Type 1

5 32 diabetes culd be explained by abnrmalities in NIMGU. In this study, ur measurement f NIMGU was made indirectly by extraplatin f measured values fr glucse uptake at nn-zer insulin levels. This derivatin depends n the assumptin that glucse uptake cntinues t vary linearly with the plasma insulin level at lw plasma insulin cncentratin. Tw lines f evidence supprt this assumptin. In viv, glucse uptake varies linearly with plasma insulin between insulin cncentratins f I t 46 ~U/ml [2, 21]. In vitr, glucse uptake has als been shwn t be linear ver insulin cncentratins ranging frm t 25 ~U/ml [22-24]. As has been demnstrated previusly [2], it thus seems reasnable t assume that glucse uptake in viv varies linearly with plasma insulin even at lw plasma insulin cncentratins. We have demnstrated that in Type 1 diabetes glucse uptake, bth insulin mediated and nn-insulin mediated can be described by Michaelis-Menten kinetics. Specifically, we bserved a linear relatinship between glucse uptake and glucse uptake/plasma glucse (Eadie Hfstee analysis) fr plasma insulin cncentratins f, 4, 8 and 16 ~tu/ml. Insulin increased the Vmax fr glucse uptake withut changing the Km. This characteristic f glucse uptake has been described previusly in nn-diabetic subjects [2], where it was interpreted t mean that insulin augments glucse transprt slely by increasing the number f effective glucse transprters. Table 3 summarises values fr Vmax and Km fr glucse uptake in the present study and values reprted fr nn-diabetic subjects [2]. Values fr Vmax are smewhat lwer fr the Type 1 diabetic subjects, especially at the higher insulin levels. This may be explained by the fact that at the higher insulin cncentratins the %NIGMU is less (Table 2), and the majrity f glucse uptake ccurs thrugh insulin mediated mechanisms. The values fr Km fr glucse uptake fr bth Type 1 diabetes and nn-insulin subjects are similar, suggesting that the glucse transprt system is intact in these subjects with Type I diabetes. Of nte is the fact that ur research subjects had an average haemglbin Alc f 7.2% (nrmal less than 6%). Thus they were in relatively gd glycaemic cntrl. It is, therefre, pssible that the glucse transprt system is still nrmally perative in well cntrlled Type 1 diabetic subjects whereas this may nt be demnstrated in thse subjects in prer glycaemic cntrl. In additin, it must be remembered that thse subjects with a haemglbin Alc that is exceedingly elevated may have ther abnrmalities f intermediary metablism that wuld interfere with glucse metablism and hence the results and interpretatins. In the pst-absrptive state in nn-diabetic subjects, NIMGU accunts fr apprximately 75 t 85% f ttal glucse uptake [2]. In Type 1 diabetes, the crrespnding figure has been reprted t be 71% [3]. S. L. Shumak et al.: Determinatin and kinetic analysis Table 3. Values fr Km and Vmax btained in nn-diabetic subjects (2) and the present study. FIRI -- free immunreactive insulin (~tu/ml) FIRI Km (mml/l) Vmax (mml- kg- 1. m- 1) Nn-diabetic Type 1 diabetic Nn-diabetic Type 1 subjects patients subjects diabetic patients In ur subjects with Type 1 diabetes, we have shwn that apprximately 85 t 9% f glucse uptake is nninsulin-mediated during the lw insulin infusin rate (plasma insulin cncentratins gu/ml). These plasma insulin levels were higher than thse present in the basal state (after vernight euglycaemia, preclamp). Thus, the %NIMGU in ur subjects in the pst-absrptive state may have been slightly greater than 85-9%. Hwever, the fact that NIMGU in Type 1 diabetes is quantitatively similar t that in nndiabetic subjects reprted in the literature t suggests that abnrmalities f insulin sensitivity in Type 1 diabetes may be secndary t defective insulin actin and are nt due t an irreversible defect in the glucse transprt system. Acknwledgements. These studies were supprted by the Canadian Diabetes Assciatin and Munt Sinai Hspital Research Fund (ISG). In additin, S. L. S. was the Cnnaught Nv Research Fellw f the Canadian Diabetes Assciatin. We thank B.E. Nble, RN whse dedicatin made these studies pssible and the technical staff f the Banting and Best Diabetes Cre Labratry. We thank Ms. M. Marczak and Ms. D. Orlans fr secretarial assistance. References 1. Bergman RN, Finegd DT, Ader M (1985) Assessment f insulin sensitivity in viv. Endcr Rev 6: Gttesman I, Mandarin L, Gerich J (1983) Estimatin and kinetic analysis f insulin-independent glucse uptake in human subjects. 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6 S. L. Shumak et al.: Determinatin and kinetic analysis 33 istics fr the effect f insulin n prductin and utilizatin f glucse in man. Am J Physi124:E63-E Sherwin RS, Kramer KJ, Tbin JD, Insel PA, Liljen Quist JE, Betman M, Andres R (1974) A mdel f the kinetics f insulin in man. J Clin Invest 53 : McGuire E, Helderman J, Tbin J, Andres R, Berman M (1976) Effects f arterial versus venus sampling n analysis f glucse kinetics in man. J Appl Physi141 : Desbuquis B, Auerbach GD (1971) Use f plyethylene glycl t separate free and antibdy-bund peptide hrmnes in radiimmunassays. J Clin Endcrinl Metab 33: Hanna AK, Zinman B, Nakhda AF, Minuk HL, Stkes EF, A1- bisser AM, Leibel BS, Marliss EB (198) Insulin, glucagn and aminacids during glycemic cntrl by the artificial pancreas in diabetic man. Metablism 29: Rizza R, Mandarin L, Gerich J (1981) Mechanism and significance f insulin resistance in nninsulin-dependent diabetes mellitus. Diabetes 3: DeBd R, Steele R, Alstszuler N, Dunn A, Bishp J (1963) On the hrmnal regulatin f carbhydrate metablism: studies with C14-glucse. Recent Prg Res 19: Dunn A, Katz J, Glden S, Chenweth M (1976) Estimatin f glucse turnver and recycling in rabbits using varius [3H14C] glucse labels. Am J Physil 23: Radziuk J, Nrwich KH, Vranic M (1978) Experimental validatin f measurements f glucse turnver in nnsteady state. Am J Physil 234:E84-E Cushman S, Wardzala L (198) Ptential mechanism f insulin actin n glucse transprt in the islated rat adipse cell. Apparent translcatin f intracellular transprt systems t the plasma membrane. J Bil Chem 255: Karnielli E, Hissin P, Simpsn I, Salans L, Cushman S (1981) A pssible mechanism f insulin resistance in the rat adipse cell in streptztcin-induced diabetes mellitus. J Clin Invest 68: Gttesman I, Mandarin L, Verdnk C, Rizza R, Gerich J (1982) Insulin increases the maximum velcity fr glucse uptake withut altering the Michaelis cnstant in man. J Clin Invest 7: Best JD, Tabrsky GJ Jr, Halter JB, Prte D Jr (1981) Glucse dispsal is nt prprtinal t plasma glucse level in man. Diabetes 3: Ciaraldi T, Klterman O, Siegal J, Olefsky J (1979) Insulin-stimulated glucse transprt in human adipcytes. Am J Physil 236: E621-E LeMarchand-Brustel Y, Freychet P (1979) Effect f fasting and streptztcin diabetes n insulin binding and actin in the islated muse sleus muscle. J Clin Invest 64: Berhanu P, Olefsky J (1981) Effects f insulin and insulin-like agents n the glucse transprt system f cultured human fibrblasts. Diabetes 3: Received: 9 May 1988 and in revised frm: 23 Nvember 1988 Dr. I. Gttesman 23 Eglintn Avenue West Suite 56 Mississauga, Ontari L5M 2V8 Canada