3.1. In liver cirrhosis, hepatic magnesium content is lower and TRPM7 expression in hepatocytes is higher than in healthy liver.
Table 1 shows the demographic and clinical characteristics of cirrhotic patients in study populations A and B and their respective healthy liver donor control groups.
The only significant difference between the two populations of cirrhotic patients was the lower frequency of viral etiology of the disease in study population B compared to study population A, while no difference was present for age, sex, BMI, Metabolic associated fatty liver disease (MAFLD) and alcoholic etiology of cirrhosis, HCC, diuretic treatment, serum aminotransferase activities, MELDNa both at listing and at transplant, length of time on the waiting list and Δ-MELDNa. The two populations of cirrhotic patients did not differ from the respective healthy liver donor control groups for age, sex, BMI and serum aminotransferase activities. The median content of Mg, measured in biopsies of liver tissue using atomic absorption spectrometry, was significantly (P <0.001) lower in cirrhotic patients of the study population A [117.2 (IQR 110.5-132.9) μg / g w.w.] compared to its healthy liver donor controls group [162.8 (IQR 155.9-169.8) μg / g w.w.] (
Figure 2).
Regarding TRPM7 expression, human salivary glands with highly positive cells with large cytoplasmic granules (
Figure 3, panel A) were considered as a positive control. Then, we applied a semiquantitative scoring system by calculating the percentage of hepatocytes with intense or weak staining in cirrhotic and control donor livers. Considering cirrhotic liver samples from study population B (
Figure 3 panels B, C), 81% showed intense staining in some hepatocytes, with up to 31% of hepatocytes affected. Weak staining affected all cirrhotic liver samples and 45% of these had at least half of the hepatocytes affected. In contrast, in donor control livers, only 30% of samples showed intense staining in some hepatocytes, with up to 3% of hepatocytes affected. Weak staining affected all donor liver samples but only 10% of these had at least half of the hepatocytes affected.
The cirrhotic group of study population B, compared to the its healthy liver donor control group, showed significantly higher percentages of hepatocytes with intense TRPM7 staining [2.8 (0.2-9.2) vs 0.0 (0.0-1.8)%; p<0.01], with weak staining [47.4 (34.0-56.2) vs 18.8 (10.7-32.8)%; p<0.01], and with total staining, i.e. weak or intense, [53.0 (36.8-62.0) vs 20.7 (10.7-32.8)%; p<0.001] (
Figure 4 Panels A-C).
At least 4% of hepatocytes with intense TRPM7 staining were present in 45% of the cirrhotic liver samples and in none of the donor samples. Interestingly, in donor livers the percentage of TRPM7 positive hepatocytes was significantly lower (p=0.01) in those without any histological sign of inflammation [10.3 (IQR 8.4-13.3)%; n=4] versus those with mild inflammation [30.0 (IQR 21.2-43.6)%; n=6].
In liver cirrhosis, MELDNa at the time of liver transplantation is inversely correlated with the content of magnesium in liver tissue and hepatocytes and directly with the hepatocellular expression of TRPM7.
In cirrhotic patients of study population A, the MELDNa score measured at the time of liver transplant correlated inversely with the content of Mg measured in liver biopsies using atomic absorption spectrometry (
Figure 5, panel A). To verify if this inverse correlation was retained, we used X-ray Fluorescence technique, an analytical method that allowed measuring Mg inside the hepatocytes in 15 cirrhotic patients of study population B. The significant inverse correlation between MELDNa and hepatocyte content of Mg measured at TwinMic beamline (r = -0.531; p = 0.042;
Figure 5, panel B) and, in 7 of these patients, measured at XRF beamline (r = -0.854; p = 0.014) (
Figure 5, panel C) was confirmed. Furthermore, the MELDNa score of study population B correlated directly with the percentage of hepatocytes with intense and with total, i.e. sum of intense and weak, staining for TRPM7 (
Figure 5, panels D and E). No correlation was found between MELDNa and the percentage of hepatocytes weakly stained for TRPM7.
We then wanted to verify whether the correlations of the MELDNa values with Mg content in liver biopsies and with the hepatocellular expression of TRPM7 were independent of confounders. To do this we first analyzed whether, within each of the two cirrhotic study populations, patients differed when subgrouped into low and high MELDNa, based on their respective median MELDNa value (
Table 2).
As expected, in the study population A, patients with high MELDNa had significantly lower Mg content than the low MELDNa group. In study population B, patients with high MELDNa showed a significantly higher proportion of hepatocytes with intense and total TRPM7 staining than those with low MELDNa. No intergroup difference in study population B was found with regard to the percentage of hepatocytes with weak TRPM7 expression. Furthermore, in both study populations A and B (
Table 2), patients with lower MELDNa had a significantly higher frequency of HCC and a lower frequency of diuretic treatment compared with patients with higher MELD. No intergroup differences were present for age, sex, BMI and etiology of cirrhosis. The serum Mg concentration, available only for study population B, did not differ in patients with low compared to high MELDNa. The inverse correlation between MELDNa and the Mg content measured in liver biopsies and the direct correlations between MELDNa and the percentage of hepatocytes with intense or total TRPM7 staining were significant also performing multiple linear regression (
Table 3).
Finally, in the cirrhotic study population B, the serum Mg concentration correlated directly (r = 0.553; P = 0.033) with the Mg content in hepatocytes measured at the TwinMic beamline (
Supplementary Figure S1), but did not correlate with any degree of TRPM7 expression. Furthermore, TRPM7 expression did not correlate with hepatic Mg content, measured at both Elettra Synchroton TwinMic and XRF beamlines.
In liver cirrhosis, serum AST activity at the time of liver transplantation is inversely correlated with magnesium content in liver tissue and hepatocytes and directly with hepatocellular expression of TRPM7.
In cirrhotic patients of the group “study population A”, the serum activity of AST at transplant, but not that of ALT, was inversely correlated with the Mg content measured in liver biopsies using atomic absorption spectrometry (r = -0.458; p = 0.016;
Figure 6, panel A). In cirrhotic patients of study population B, the serum activity of AST at transplant, but not that of ALT, was inversely correlated with the content of Mg in hepatocytes measured using both the TwinMic (r = -0.615; p = 0.015;
Figure 6, panel B) and XRF beamlines (r = -0.758; p = 0.048;
Figure 6, panel C). In the cirrhotic patients of the group “study population B”, serum activity of AST directly correlated with the percentage of both high intensity (r=0.511; p=0.003;
Figure 5 panel D) and total (r=0.428; p=0.016;
Figure 5 panel E), but not with the percentage of weakly TRPM7 positive hepatocytes. Serum activity of ALT directly correlated with the percentage of both high intensity (r=0.439; p=0.013) and total (r=0.396; p=0.028), but not with the percentage of weakly TRPM7 positive hepatocytes.
We then wanted to verify whether the correlations of the serum AST activity with Mg content in liver biopsies and with the hepatocellular expression of TRPM7 were independent of confounders. To do so we first analyzed whether, within each of the two cirrhotic study populations, patients differed in clinical and demographic characteristics when grouped according to the respective AST median value (
Supplementary Table S1). In the group “study population A”, the content of Mg measured in liver biopsies using atomic absorption spectrometry did not differ between the group with low and high AST serum activity. In the group “study population B”, compared to patients with lower values, those having high AST activity showed a significantly higher percentage of hepatocytes with intense, but not weak or total TRPM7 staining. No intergroup differences were present for sex, BMI, etiology of cirrhosis and diuretic use in both study populations. The serum Mg concentration, available only for study population B, did not differ in patients with low compared to those with high serum AST. The inverse correlation between serum AST activity and the Mg content measured in liver biopsies and the direct correlation between AST serum activity and the percentage of hepatocytes with intense, but not total, TRPM7 staining remained significant even at multiple linear regression (
Table 4).
In liver cirrhosis the worsening of MELDNa during the waitlist time is inversely correlated with the content of magnesium in biopsies of liver tissue and directly with the hepatocellular expression of TRPM7 at the time of liver transplantation.
In cirrhotic patients, the MELDNa data were available not only at the time of liver transplant but also at the time of waitlisting, allowing the calculation of Δ-MELDNa. Δ-MELDNa correlated negatively with the content of Mg in liver biopsies measured using atomic absorption spectrometry in the group “study population A” (r=-0.404; p=0.037), while no significant correlation was found in study population B measuring Mg liver content at both TwinMic (r=-0.367; p=0.178) and XRF beamlines (r=-0.652; p=0.112). In the cirrhotic patients of the group “study population B”, Δ-MELDNa directly correlated with the percentage of both high intensity (r=0.569; p=0.001) and total (r=0.402; p=0.025), but not with the percentage of weakly stained, TRPM7 positive hepatocytes assessed at liver transplant.
We then wanted to verify whether the correlations of Δ-MELDNa with Mg content in liver biopsies measured using atomic absorption spectrometry and with the expression of TRPM7 were independent of confounders. To do so we first analyzed whether, within each of the two cirrhotic study populations, patients differed in clinical and demographic characteristics when grouped according to the respective Δ-MELDNa median value (
Supplementary Table S2). In the group “study population A”, the content of Mg measured in liver biopsies did not differ in the groups having low or high Δ-MELDNa. In study population B, patients with high compared to those with low Δ-MELDNa showed a significantly higher percentage of hepatocytes with intense and total, but not weak, TRPM7 staining. No intergroup differences were present for sex, BMI, etiology of cirrhosis and diuretic use in both study populations. The serum Mg concentration, available only for study population B, did not differ in patients with low compared to those with high Δ-MELDNa. At multiple linear regression introducing age, presence of HCC, serum Mg concentration, diuretic treatment as covariates in the initial backward elimination model, the direct correlation between Δ-MELDNa and the percentage of hepatocytes with intense (B=0.436; 95% CI of B=0.179 — 0.670; P=0.009) and with total TRPM7 staining (B=0.153; 95% CI of B=0.054 — 0.270; P=0.025) remained significant. On the contrary the Mg liver content was not significantly associated with Δ-MELDNa at multiple linear regression.