THE EFFECT OF LOSARTAN ON INSULIN RESISTANCE AND BETA CELL FUNCTION IN CHRONIC HEMODIALYSIS PATIENTS

Abstract

Insulin resistance (IR) is prevalent in hemodialysis patients. IR and hyperinsulinemia have an important role in the development of atherosclerosis, which is the most common cause of morbidity and mortality in hemodialysis patients. Thus, antihypertensive drugs that lower IR, may have an additional beneficial effect in the treatment of cardiovascular diseases in these patients. In this preliminary study we examined the effect of Losartan (an angiotensin II receptor antagonist) treatment on IR and beta cell function in five hypertensive non-diabetic chronic hemodialysis patients. All other known causes of IR in end stage renal failure were excluded. After a washout period of two weeks, Losartan 50 mg, was administered for 6 weeks. Fasting blood glucose (FBG) and insulin levels were measured before and after the treatment IR and beta cell function were calculated using the “homeostasis model assessment”-HOMA. Systolic and diastolic blood pressure (BP) have not changed significantly throughout the study. FBG increased significantly from 76 mg/dL ± 1 to 89 mg/dL ±4 (p < 0.01), however, insulin levels have not changed significantly. Calculated IR values did not show a difference, but calculated beta cell function decreased significantly after Losartan treatment from 291% ± 50 to 146% ± 10, (p < 0.016). These preliminary results suggest that in chronic hemodialysis hypertensive non-diabetic patients short treatment with Losartan has deleterious effect on glucose homeostasis mediated via a decrease in beta cell function

• Insulin resistance
• Beta cell function
• Angiotensin II receptor antagonist
• Hemodialysis
• Hypertension
• Homeostasis model assessment

INTRODUCTION

Insulin resistance (IR) is a known complication of end stage renal failure and is prevalent in hemodialysis patients [[1]]. Numerous factors are believed to contribute to this phenomenon in uremic patients such as hyperparathyroidism [[2]], anemia [[3]] uremic toxins [[1]] inadequacy of dialysis. Despite some evidence that IR improves after the initiation of hemodialysis [4-5], correction of anemia by erythropoietin [[3]] and treatment of hyperparathyroidism mainly by 1–25 vitamin D [[2]], [[6]], IR usually still exists. Moreover, hyperinsulinemia and IR have an important role in the pathogenesis of atherosclerosis and cardiovascular diseases [[7]], [[9]] which are leading causes of morbidity and mortality in chronic hemodialysis patients [[10]]. Some antihypertensive drugs such as calcium channel blockers [[11]], angiotensin converting enzyme inhibitors [[12]] and alpha receptor antagonists [13-14] may have beneficial effects on IR in hypertensive patients. It has been demonstrated that angiotensin II receptor antagonists (AIIA) improve glucose metabolism in hypertensive patients with normal renal function. It is suggested that the drug by a sympathiolytic effect, lowers blood viscosity, causes vasodilatation, and improves insulin sensitivity [15-17]. However, the effect of AIIA has not been studied in hypertensive hemodialysis patients. The aim of this study was to evaluate the effect of Losartan- an AIIA, on IR and beta cell function in hypertensive non-diabetic chronic hemodialysis patients.

METHODS

Patients

Two groups of chronic hemodialysis patients (for at least 6 months) were included in the study: hypertensive patients (systolic blood pressure (BP) ≥ 140 or diastolic BP ≥ 90 mmHg) treated by only one drug, and recently diagnosed (two-month) untreated hypertensive patients. All patients had hematocrit ≥ 35, transferrin saturation ≥ 20%, KT/V ≥ 1.1 and parathyroid hormone (PTH) levels not above twice the upper limit range. Diabetic patients as determined by oral glucose tolerance test (OGTT) and patients with known chronic liver diseases or patients who were positive for HBs antigen, anti HCV or HIV were excluded.

Methods and Study Protocol

Patients gave their informed consent and the study was approved by the local ethics committee. Antihypertensive medications were stopped and after a washout period of two weeks the patients were examined and blood pressure was measured. Three consecutive blood samples (five minutes apart) for the analysis of glucose and insulin were drawn 24 h after the last hemodialysis session and following 12 h fast. Blood samples were analyzed for total cholesterol, high density lipoprotein (HDL), triglycerides (T.G), aspartate aminotransferase (AST), alanine aminotransfarase (ALT), complete blood count, transferrin saturation, PTH levels as well. Thereafter patients started the active treatment of losartan (50 mg once a day). Following 6 weeks of treatment the patients were reevaluated and blood was drawn for the same parameters. Insulin levels were measured by commercially available solid phase radioimmunoassay, maximal sensitivity 1.2 μU/mL (Diagnostic Products Corp. LA USA). PTH levels were measured by commercially available two-site fluid phase immunoradiometric assay specific for the intact 84 aminoacid chain of PTH, maximal sensitivity 1 pg/mL (Nichols Diagnostic CA USA).

Insulin resistance and the beta cell function were calculated by the three-sample mean of fasting blood glucose and insulin levels, according to the “homeostasis model assessment” (HOMA) [[18]]. The model based on the assumption that the level of serum glucose is determined by the combination of beta cell function and insulin resistance/sensitivity. For each individual the model determines the beta cell function and insulin sensitivity that uniquely predict the measured fasting glucose and insulin concentrations. Results are expressed as a percentage of values in lean reference population. The final equations of the model are:

1. IR = insulin/(22.5ex^{−ln glucose})

2. Beta cell function (%) = 20 insulin/(glucose-3.5)

Statistical Analysis

Results are expressed as the mean ± SEM.

Two-tailed Mann Whitney U test was performed to evaluate the significance of the results.

RESULTS

Five patients were included in the study; their characteristics are shown in Table 1. No reduction in BP was observed (Table 2). Mean fast blood glucose (FBG) level increased significantly after the treatment with Losartan (Table 3). Mean Insulin level did not change significantly (Table 3). Mean calculated IR, by HOMA, did not change significantly before and after the treatment (1.9 ± 0.06 vs. 2.1 ± 0.1 respectively, p= NS). In contrast mean calculated Beta cell function value decreased significantly after drug treatment. (from 291% ± 50 to 146% ± 10 p< 0.016). Other laboratory parameters: total cholesterol, T.G, L.D.L, H.D.L did not change (Table 2). No adverse effects to Losartan treatment were noted.

Table 1. Patients Characteristics

5	4	3	2	1
67/M	71/M	66/F	56/F	73/M	Age/sex
APCKD	R″A, NSAID	HTN	APCKD	familial nephritis	renal disease
peptic d.	IHD, COPD	hypothyroidsm		COPD, peptic d.	other disease
20 m	18 m	16 m	11 m	4.5 y	time on hemodialysis
fam, vit D,	ben, asp,	vit D, Ca,	dil, vit D,	fam, ben,	drugs
Ca, Epo,	vit D,	dox, Epo,	Ca, Epo,	pra, Epo,
Fe, nif	Ca, Epo, Fe, is	Fe L.	Fe	Fe Ca
23.4	25.8	22.4	21.7	19.1	B.M.I kg/m^2
11.9/36.7	11.7/36.7	12.8/38.8	14.8/42.9	12.9/39	Hbgr/dL /Hct%
25.9	24.8	23.4	21.9	31.3	transferrin saturation %
21/20	4/6	9/8	13/11	14/4	GOT/GPT (U/L)
11.1	19	8	7.8	16	PTH (ng/L)
1.3	1.15	1.2	1.3	1.1	KT/V

HTN-hypertension, R″A-rheumatoid arthritis, NSAID-non steroid anti inflammatory drugs, APCKD-adult polycystic kidney disease, IHD-ischemic heart disease, COPD-chronic obstructive pulmonary disease, fam-famotidine, ben-benazepril, pra-pravastatin, Fe-ferrum sacharate, Epo-erythropoietin, Ca-calcium carbonate, vit D-1α hydroxy vit D3, dil-diltiazem, dox-doxazocin, L-Eltroxin, asp-aspirin, is-isosorbide dinitrate, nif-nifedipine.

Table 2. Blood Pressure and Lipid Profile Before and After Losartan Treatment

	Before Losartan Treatment (mean ± SEM)	After Losartan Treatment (mean ± SEM)	p value
Systolic BP (mmHg)	148 ± 2	148 ± 9	NS
Diastolic BP (mmHg)	74 ± 5	73 ± 11	NS
Cholesterol mg/dL	204 ± 28	198 ± 22	NS
(mmol/L)	(5.27 ± 0.7)	(5.12 ± 0.6)
HDL mg/dL	58 ± 16	63 ± 14	NS
(mmol/L)	(1.5 ± 0.4)	(1.63 ± 0.4)
LDL mg/dL	126 ± 25	118 ± 17	NS
(mmo/L)	(3.25 ± 0.6)	(3.1 ± 0.4)
TG mg/dL	107 ± 28	119 ± 30	NS
(mmol/L)	(1.2 ± 0.3)	(1.34 ± 0.3)

BP = blood pressure; TG = triglyceride; NS = not significant.

Table 3. Insulin and Glucose Concentrations Before and After Losartan Treatment

Patient No.	Glucose Before Treatment mg/dL (mmol/L)	Glucose After Treatment mg/dL (mmol/L)	Insulin Before Treatment μU/mL (pmol/L)	Insulin After Treatment μU/mL (pmol/L)
1	80.7 (4.5)	83.7 (4.6)	11.5 (82.5)	10.4 (74.6)
2	69.7 (3.9)	104 (5.8)	10.1 (72.5)	8.5 (61)
3	80.7 (4.5)	87.3 (4.8)	9.87 (70.8)	8.1 (58.1)
4	69.7 (3.9)	87.3 (4.8)	9.57 (68.7)	10.4 (74.6)
5	81 (4.5)	87.6 (4.9)	9.56 (68.6)	10.2 (73.1)
Mean ± SEM	76 ± 1	89 ± 4	10.12 ± 0.4	9.35 ± 0.6
	(4.2 ± 0.1)^*	(5 ± 0.2)^*	(72.6 ± 2.29)	(68.2 ± 4.3)

Every value of insulin and glucose concentration is the mean of three consecutive samples taken in 5 min intervals.

^*p < 0.01.

DISCUSSION

Our preliminary data demonstrate that 6 weeks treatment with the AIIA drug Losartan resulted in a significant increase in FBG in chronic hemodialysis hypertensive non-diabetic patients. Beta cell function was decreased while IR remained unaltered. This may suggest that Losartan directly suppress beta cell secretory function with no detectable effect on insulin sensitivity in peripheral insulin responsive tissues. Our findings have important implications in hemodialysis patients inasmuch as IR is a known complication of end stage renal failure. These patients who are often hypertensive and especially prone to cardiovascular diseases are increasingly treated with AIIA. The drugs became popular in dialysis patients in light of several studies demonstrating their ability to ameliorate glucose metabolism and reduce IR. It was suggested that Losartan, favorable effects on glucose homeostasis are mediated mainly via its sympathiolytic effect resulting in lower blood viscosity, enhanced vasodilation and decreased BP [15-17]. These effects were not detected in our patients although a comparable treatment regimen with Losartan was employed [[15]], [[17]]. However, the previous studies were conducted in patients with normal renal function as opposed to our end stage renal failure patients. The latter patients are characterized by altered glucose metabolism and insulin sensitivity [[1]].

We employed the HOMA model in order to evaluate the IR and beta cell function in our patients. There are no studies reporting the efficacy of the HOMA model for the analysis of IR and beta cell function in patients with end stage renal failure. However this model is well correlated with euglycemic clamp technique employed in other studies in order to assess the effects of AIIA on insulin sensitivity in hypertensive and uremic subjects [[1]], [[5]], [[18]]. It should be noted that the model is less precise when applied to small patient's populations and may lack the required sensitivity to detect a change in IR in our small group of patients. In addition, studies demonstrating the beneficial effect of Losartan on IR recruited patients with moderate and/or severe hypertension who exhibited significant reduction in BP following treatment [[15]], [[17]]. In contrast, our study group consisted of patients with mild isolated systolic hypertension, which did not significantly change after treatment. Thus, it is possible that Losartan mediated decrease on IR is restricted to a subgroup of patients characterized by advanced hypertensive disease and is associated with a demonstrable decrease in BP. This hypothesis remains questionable in view of two other recent reports showing that treatment with Losartan (50 mg per day) for 6 to 12 weeks had no effect on insulin sensitivity in patients with mild to moderate hypertension who demonstrated a significant reduction of their BP [19-20].

Taken together, our preliminary results based on small groups of patients suggest that in hypertensive hemodialysis patients Losartan has a deleterious effect on glucose homeostasis with no detectable effect on their BP. This effect is probably mediated via a decrease in beta cell function. The applicability of these results to other patients with milder degree of chronic renal failure or non-uremic hypertensive patients, remains unclear. Further evaluation of the effect of AIIA on hemodialysis patients by larger number of patients and longer treatment periods are necessary.