Objectives: This prospective study aimed to compare changes in serum thiamine and pyridoxine levels of patients who underwent liver transplant or living donor hepatectomy.

Materials and Methods: Between January 2013 and November 2013, 35 patients with chronic liver disease who underwent liver transplant (the recipient group) and 30 healthy individuals who underwent living donor hepatectomy (the control group) during the same period were prospectively compared in terms of both preoperative and postoperative serum thiamine and pyridoxine levels. The groups were also subjected to intragroup analysis of preoperative and post-operative changes in serum vitamin levels to determine how a major surgical procedure affected serum vitamin levels. Mann-Whitney U test and Wilcoxon signed-rank test were used for intergroup comparisons and intragroup repeated measurements, respectively.

Results: The intergroup comparisons revealed significant differences in favor of the control group with respect to preoperative thiamine (P < .026) and postoperative thiamine (P < .017) levels, whereas there were statistically significant differences in favor of the recipient group with respect to the preoperative pyridoxine (P < .006) and postoperative pyridoxine (P < .001) levels. The intragroup comparisons showed significant increases in serum thiamine (P < .001) and pyridoxine (P < .031) levels compared with the preoperative serum levels of both vitamins at postoperative day 5 in the recipient group. In the control group, serum thiamine level (P < .001) at postoperative day 5 was significantly different from the preoperative level. On the other hand, a drop in serum pyridoxine level was detected at postoperative day 5, although this was not statistically significant (P < .21).

Conclusions: This study showed a lower serum thiamine level but a higher serum pyridoxine level in patients with chronic liver disease versus healthy controls. This difference persisted into the early postoperative period. This study also showed significant increases in thiamine and pyridoxine levels after transplant surgery.

Key words : Chronic liver disease, Liver transplantation, Living donor hepatectomy, Metabolism

Introduction

Chronic liver disease is characterized by progressive destruction of liver parenchyma and, depending on the cause and disease stage, may lead to metabolism deficits of many nutrients, including slowed conversion of vitamins into active metabolites. So far, many studies have been published on the effects of chronic liver disease on fat-soluble vitamins such as vitamins D and K.^1,2 Similar studies have also been conducted on water-soluble, relatively less stored vitamins, including vitamin B (thiamine) and B6 (pyridoxine).^3,4 Irrespective of the underlying disorder, chronic liver disease has been shown to cause severe deficits in the metabolism of many vitamins, including pyridoxine and thiamine.³

Thiamine is a particularly important vitamin because it acts as a cofactor in pyruvic acid decar-boxylation, alpha ketoglutaric acid decarboxylation, and hexose monophosphate shunt. Hence, its deficiency has a variety of clinical consequences.3 The most common causes of thiamine deficiency include poor nutrition, inadequate absorption of nutrients from the intestinal system, and hemodialysis. The association between chronic liver disease and reduced serum thiamine concentration has been investigated for decades, and 80% of patients with chronic alcoholism have been shown to have thiamine deficiency.^3,5 This association has been traditionally explained by reduced thiamine depots because of alcohol use or inadequate nutrition. An association between thiamine deficiency and liver disease has also been shown in nonalcoholic liver disease.³ In this disorder, thiamine deficiency may occur as a result of impaired metabolism, depletion of thiamine depots, reduced hepatic cell count, and impaired intestinal vitamin absorption due to disrupted splanchnic blood flow. Pyridoxine, when orally ingested, is rapidly converted by the liver to pyridoxal-5-phosphate, an active coenzyme that plays a vital role in many bodily mechanisms, notably amino acid metabolism.⁶ The major functions of pyridoxine include amino group transfer between amino acids, neurotransmitter biosynthesis, conversion of tryptophan into niacin, and hemoglobin synthesis. In 60% to 90% of patients with cirrhotic liver disease, pyridoxal-5-phosphate/pyridoxine levels show fluctuations, mostly due to a reduction of the conversion of pyridoxine into pyridoxal-5-phosphate.^4,6-8 Factors such as inadequate dietary pyridoxine intake, impaired intestinal absorption, and a greater rate of pyridoxal-5-phosphate degradation compared with healthy individuals are other reasons of pyridoxine deficiency in patients with chronic liver disease.² Hence, many biochemical mechanisms may slow in patients with liver disease, depending on the severity of pyridoxine deficiency. Herein, we aimed to determine the alterations in serum thiamine and pyridoxine levels in both chronic liver disease and at the early posttransplant period.

Materials and Methods

The primary objective of this prospective study was to determine the changes in serum thiamine and pyridoxine levels in patients scheduled for liver transplant for chronic liver disease. For this investigation, patients who underwent liver transplant for chronic liver disease at Inonu University Liver Transplantation Institute between January 2013 and November 2013 were grouped as the recipient group (n = 40). The control group included 40 healthy individuals who underwent living donor hepatectomy at the same period after being examined for living donor candidacy. Five individuals from the recipient group and 10 from the control group were excluded due to various problems, including wrong barcode printing, loss of samples, and breakage of tubes during blood sample transport. As a result, our total study group included 65 patients (35 in the recipient and 30 in the control group) who were suitable for study entry.

Blood samples were obtained from patients in both groups both before anesthesia induction and 5 days after the surgical procedure. The samples were transported to the laboratory in maintained cold (cold chain). We used EDTA-containing purple cap tubes for thiamine measurement. After blood samples were centrifuged, plasma samples were analyzed. For pyridoxine samples, we used EDTA-containing purple cap tubes, but these were not centrifuged. The blood samples were analyzed by the Delta Analysis Laboratory (Ankara, Turkey). Both thiamine and pyridoxine levels were determined with a Shimadzu high-performance liquid chromatography (Shimadzu Corporation, Japan) device and use of the ImmuChrom kit (Immuchrom GmbH, Heppenheim, Germany). The reference levels for thiamine and pyridoxine are 35 to 99 ng/mL and 3.6 to 18.1 ng/mL, respectively.

Our secondary aim was to determine whether significant changes would occur in serum thiamine and pyridoxine levels after major liver surgery in recipients (native hepatectomy + liver transplant) and in control patients (donor hepatectomy). That is, we aimed to investigate whether liver surgery would have any meaningful effect on serum vitamin levels. For this purpose, we compared serum thiamine and pyridoxine levels of recipient and control groups preoperatively and at postoperative day 5. This study was approved by Inonu University Scientific Research Coordination Unit (project number 2013/127), and all patients signed the informed consent form.

Study data were analyzed with the IBM SPSS statistics software package (SPSS: An IBM Company, version 23.0, IBM Corporation, Armonk, NY, USA). Because the distribution of the continuous variables was not homogeneous, a Mann-Whitney U test was used for intergroup comparisons. The Wilcoxon signed rank test was used for intragroup repeated measurements. The intergroup differences for sex were tested with the Yates corrected chi-square test. The results are expressed as median, minimum to maximum, and mean (SD). P < .05 was considered statistically significant for all comparisons.

Results

This study included 65 patients who ranged in age from 19 to 73 years, with range of 19 to 73 years (mean [SD] of 49.3 [13.9] y) for recipients and 22 to 52 years (mean [SD] of 33 [9.3] y) for the control group. Mean age was significantly different between the groups (P < .001). The recipient group had a male percentage of 80%, and the control group had a male percentage of 56.7%, with the difference being nonsignificant (P < .078).
In recipients, preoperative serum thiamine levels ranged from 24.7 to 146.2 ng/mL (median = 84.5 ng/mL, mean [SD] = 87.1 [27.3] ng/mL). In the control group, preoperative serum thiamine levels ranged from 22 to 158 ng/mL (median = 107.6 ng/mL, mean [SD] = 102.7 [31.8] ng/mL). Results were significantly different between groups (P < .026). The recipient group had postoperative serum thiamine levels ranging between 45 and 219 ng/mL (median = 108 ng/mL, mean [SD] = 112.7 [39.1] ng/mL), whereas the control group had postoperative serum thiamine levels ranging between 81.4 and 250 ng/mL (median = 124.8 ng/mL, mean [SD] = 129.7 [36] ng/mL); differences were statistically significant (P < .017). Both preoperative and postoperative serum thiamine levels were significantly higher in the control group.

In the recipient group, preoperative serum pyridoxine levels ranged between 1 and 21.1 ng/mL (median = 3.9 ng/mL, mean [SD] = 4.98 [3.75] ng/mL), whereas the control group had preoperative pyridoxine levels ranging between 1 and 8.9 ng/mL (median = 3 ng/mL, mean [SD] = 3 [1.76] ng/mL); results were significantly different (P < .006). Regarding postoperative pyridoxine levels, the recipient group had results that ranged between 1.3 and 16.4 ng/mL (median = 5.75 ng/mL, mean [SD] = 7.2 [4.4] ng/mL), whereas the control group had results that ranged between 1.1 and 6 ng/mL (median = 2.25 ng/mL, mean [SD] = 2.6 [1.3] ng/mL). These results were significantly different between groups (P < .001). Thus, the recipients had significantly higher preoperative and postoperative serum pyridoxine levels.

Intragroup repeated measures (ie, the pre- and postoperative serum levels) were analyzed using the Wilcoxon signed rank test to determine whether major liver surgery had any meaningful effect on serum thiamine and pyridoxine levels. Accordingly, both postoperative serum thiamine (P < .001) and postoperative serum pyridoxine levels (P < .031) were significantly increased compared with the preoperative serum levels in the recipient group. Similarly, the control group showed a significantly greater serum thiamine level postoperatively (P < .001) than shown preoperatively. In contrast, we observed a decrease in postoperative serum pyridoxine level compared with the preoperative serum pyridoxine level, although this difference was not statistically significant (P < .21). The demographics and laboratory results of the groups and their statistical analyses are summarized in Table 1.

Discussion

When we considered the reference range for thiamine (35-99 ng/mL), only 1 patient from the recipient and 1 patient from the control group showed serum levels below the lower reference limit. Compared with the recipient group, control patients had a greater preoperative thiamine level. A similar statistical significant difference was also observed for postoperative serum thiamine levels. Two interpretations can be made with regard to these results. First, although the thiamine level is markedly reduced in chronic liver disease versus that shown in healthy individuals, it was not reduced below the lower reference limit. Second, because we did not have long-term outcome data, we were unable to make an interpretation regarding how liver transplant alters serum thiamine levels over time. However, one should not overlook the contribution of some other factors, such as the normalization of the gastrointestinal system after healthy liver transplant and a lowering portal pressure in the recipient group.

A search of the English medical literature on PubMed and Google Scholar databases using the key words of thiamine, chronic, liver, and disease in various different combinations revealed no study that compared thiamine levels of patients with chronic liver disease versus healthy individuals. As far as we know, our study is the first in the literature in this regard, and thus we were unable to find another study for comparison. Levy and associates5 grouped their patients into 3 groups: those with alcoholic cirrhosis (n = 40), those with hepatitis C virus-related cirrhosis (n = 48), and those with chronic hepatitis C virus without cirrhosis (n = 59). The investigators did not detect any significant differences between the groups with respect to thiamine levels. They also reported no correlation between disease severity and vitamin thiamine levels.

When we considered the reference range for pyridoxine (3.6-18.1 ng/mL), the serum pyridoxine level was below the lower limit in 15 patients in the recipient group and 22 patients in the control group. Interestingly, the recipient group, when compared with control individuals, had a higher preoperative pyridoxine level. A statistically significant difference was found for postoperative serum pyridoxine levels. Although pyridoxine deficiency, seen in 42.8% of the recipient patients, can be explained by chronic liver disease, it is difficult to explain pyridoxine deficiency in 73.3% of the control group, which was entirely composed of healthy individuals.

Serum pyridoxine levels are lower than normal irrespective of the various underlying causes (see Introduction) in more than 60% of patients with chronic liver disease.⁷ However, there is a paucity of studies that compare serum pyridoxine levels of patients with chronic liver disease versus levels shown in healthy controls. Labadarios and associates⁷ showed that serum pyridoxine levels were significantly lower in patients with chronic liver disease (3.0 ± 1 ng/mL) versus their control group (11.7 ± 1 ng/mL). The authors also indicated that serum pyridoxine levels were not significantly different in patients with alcoholic versus nonalcoholic chronic liver disease.⁷ On the other hand, Zaman and associates6 demonstrated that serum pyridoxine levels were not significantly different versus levels shown in their control group. According to our results, serum pyridoxine levels at pretransplant and posttransplant were significantly higher in the recipient group than in the control group. It is difficult to interpret and explain these results, which contradict with the existing literature. However, when we consider all 3 studies together, it is clear that large-scale prospective studies are needed to elucidate the behavior of serum pyridoxine levels in chronic liver disease. Moreover, because only one of our patients had alcoholic liver disease as the underlying cause, we were unable to make any conclusions regarding the relation between alcoholic liver disease and vitamin deficits.

An additional point that needs further clarification is the significant increase in serum thiamine and pyridoxine levels at the early post-operative period after a major surgery (ie, liver transplant) in the recipient group. Similar results were also found regarding the serum thiamine levels in control patients who also underwent a major surgery (donor hepatectomy). So far, no evidence-based rationale has yet been suggested for this phenomenon in the literature. From our point of view, this increase can be explained by a greater absorption or synthesis of vitamins, which are used as cofactors and needed to a greater degree after a major surgery. Furthermore, substituting an unhealthy liver with a healthy one may also have contributed to increased vitamin levels in the recipient group. Similar results could also have been observed if we had studied other vitamins and trace elements used as cofactors in humans. In any case, it is clear that our results should be confirmed by other prospective data.

In conclusion, this study showed a higher serum pyridoxine level but a lower serum thiamine level in patients with chronic liver disease compared with healthy controls. This difference persisted during the postoperative period. Significant increases in serum thiamine and pyridoxine levels after liver transplant were also shown. However, these results should be confirmed by large-volume prospective studies.

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