Homocysteine and its associations with glutathione and blood

5.2.1. Homocysteine and its associations with cellular oxidative stress, level of vitamins and hypertension

5.2.1.1. Homocysteine, vitamins, glutathione and its redox status in patients with essential hypertension

Data for comparison of the hypertensive patients and the healthy controls are shown in Table 3.

The untreated hypertensive patients had significantly higher Hcy levels compared with the healthy controls. After adjusting Hcy for age and BMI, the difference between the cases and the controls became more pronounced (p<0.008). The untreated hypertensive patients and the normotensive controls did not differ with regard to age, T-Chol, HDL, LDL, serum creatinine, protein, RBC count, hematocrit or hemoglobin. The patients with essential hypertension had significantly higher BMI as well as elevated TG and blood glucose.

Table 3. Clinical characteristics of the study groups

BMI, kg/m² 27.7±2.0 24.7±3.0 0.0001

SBP, mmHg 147.9±12.9 117.9±10.8 0.0001

DBP, mmHg 97.1±7.3 76.9±6.7 0.0001

T-Chol, mmol/l 5.6±0.8 5.3±0.8 0.14

LDL, mmol/l 3.7±0.7 3.4±0.8 0.06

HDL, mmol/l 1.3

Glucose, mmol/l 5.6±0.4 5.0±0.4 0.0001

Protein, g/l 73.0±5.4 71.3±3.8 0.11

Creatinine, µmol/l 102.2

Hemoglobin, g/l 147.6±8.2 143.6±13.9 0.18

Hematocrit, % 43.7±2.4 42.3±3.6 0.06

As shown in Table 4, the RBC-GSH levels were significantly lower and the RBC-GSSG levels higher in the subjects with essential hypertension when compared with the age-matched controls. After adjusting RBC-GSH level for age and BMI, the difference between the cases and the controls remained significant (p<0.04). In the hypertensive patients, the RBC glutathione redox status, expressed as RBC-GSSG/RBC-GSH, was twice as high as that of the control subjects indicating cellular OxS. The groups did not differ with regard to cellular folic acid level.

Table 4. Plasma homocysteine, red blood cell glutathione and folic acid in hypertensive vs. normotensive subjects

RBC-GSH, µmol/l 744.7±298.4 1001.1±286.2 0.0005

RBC-GSSG, µmol/l 108.6

5.2.1.2. Relationship between blood pressure, homocysteine, vitamins and glutathione

In the hypertensive subjects, RBC-GSH concentration showed a negative corre-lation with SBP (r= –0.44, p<0.004, Figure 2), creatinine (r= –0.43, p<0.002), protein (r= –0.41, p<0.004) and RBC folic acid (r= –0.30, p<0.04). No correlation was detected between RBC-GSH and Hcy, (r= 0.25, p<0.09, Figure 3). For the controls, RBC-GSH correlated negatively and significantly with Hcy (r= –0.41, p<0.03, Figure 2), RBC folic acid (r= –0.49, p<0.047) and creatinine (r= –0.45, p<0.02).

The results of multiple regression analysis for the hypertensive patients are given in Table 5. Hcy, hemoglobin and protein were positively and significantly correlated with RBC-GSH level, SBP and creatinine were negatively correlated with RBC-GSH level.

0 500 1000 1500

120140160180

GSH (µmol/L)

SBP (mmHg)

Figure 2. Correlation between between red blood cell reduced glutathione and systolic blood pressure in the patients with essential hypertension (r= –0.44, p<0.004).

0 500 1000 1500

5101520

GSH (µmol/L)

Hcy (µmol/L)

hypertensives controls

Figure 3. Correlations between red blood cell reduced glutathione and plasma homocysteine in the hypertensive patients and in the controls.

In the patients with essential hypertension no correlation was detected between RBC-GSH and Hcy (r= 0.25, p<0.09). In the controls, RBC-RBC-GSH correlated negatively with Hcy (r= –0.41, p<0.03).

Table 5. The results of multiple regression analysis predicting red blood cell reduced glutathione level in the hypertensive patients

Parameter Regression

coefficient

Standard error p

SBP, mmHg –6.85 2.83 0.02

Hcy, µmol/l 934.89 379.55 0.02

Hemoglobin, g/l 13.20 4.60 0.007

Creatinine, µmol/l –1738.33 684.70 0.02

Protein, g/l 16.60 6.99 0.02

Dependent variable: RBC-GSH µmol/L (r²=0.50, F statistic 7.81, p<0.00001).

5.2.1.3. Discussion

The results of this study confirmed that RBC-GSH level was significantly lower in the middle-aged untreated essential hypertension patients compared with the age-matched controls. This correlation was independent of age and BMI. This and the about twofold elevated glutathione redox ratio could indicate the dysbalanced/alterated cellular GSH system in the hypertensive patients. Our data support the findings of several previous studies. Firstly, it was shown that hypertension is directly associated with the elevated RBC glutathione redox ratio both in gestational hypertension (Nemeth et al. 2001) and in juvenile hypertensive patients (Turi et al. 2003). Secondly, considering middle-aged persons, intracellular GSH, but not plasma GSH, is characterized by a markedly lower level (Hernanz et al. 2000).

In this study, including middle-aged persons, we found an inverse correlation between SBP and RBC-GSH. It is plausible that RBC-GSH may have relevance in the pathogenesis of hypertension. GSH depletion is known to result in perturbation of the NO system and causes severe hypertension in normal animals (Vaziri et al. 2000). Thiol supplementation with GSH, given by intra-venous infusion, selectively improves human endothelial function by enhancing NO effects (Kugiyama et al. 1998, Prasad et al. 1999). Moreover, GSH infusion causes reduction of BP in adult hypertensive patients (Ceriello et al. 1991).

Several previous studies have suggested an impact of elevated Hcy on hypertension (Kanani et al. 1999, Sheu et al. 2000, Virdis et al. 2001). How-ever, its precise role remains to be elucidated. We propose that RBC-GSH and plasma Hcy should be assessed together in middle-aged hypertensive patients. It is known that approximately half of GSH is derived via Hcy metabolism in the human body. Although univariate analysis did not reveal a linear significant correlation between RBC-GSH and Hcy, in multiple regression analysis Hcy level was significantly correlated with RBC-GSH for the hypertensive patients.

In accordance with previous studies (Kanani et al. 1999, Sheu et al. 2000, Virdis et al. 2001), this study demonstrated significantly higher plasma Hcy concentration. At the same time, the elevated Hcy level was not explainable by the effect caused by RBC folic acid deficit. An elevated level of Hcy leads to decreased GSH content, probably through different pathways. It has been reported that Hcy may induce intracellular suppression of the glutathione related antioxidant defence system, and possibly also reduce Hcy-derived-GSH synthesis (Mosharov et al. 2000). In the control group, a negative linear correlation was observed between RBC-GSH and Hcy. This is in accordance with in vitro studies, where increasing Hcy concentrations reduced intracellular GSH concentrations in endothelial cells (Hultberg et al. 1997).

5.3. The effect of antihypertensive treatment on homocysteine,