Possible Association of Elevated Plasma Levels of Growth Arrest-Specific Protein 6 and the Soluble Form of Tyrosine Kinase Receptor Axl with Low Hepatitis C Viral Load in Patients with Type 2 Diabetes Mellitus

Abstract

This study aimed to investigate the plasma levels of Gas6 and soluble Axl (sAxl) in patients with chronic hepatitis C virus (HCV) infection with and without type 2 diabetes mellitus (T2DM). The study involved four groups; 50 patients with chronic HCV, 50 patients with T2DM, 50 patients with chronic HCV and T2DM, and 31 age- and sex-matched healthy controls. T2DM was diagnosed according to American Diabetes Association criteria, HCV antibodies were detected by enzyme-linked immunosorbent assays (ELISA) and confirmed by real-time-polymerase chain reaction. Plasma Gas6 and sAxl levels were assayed in all groups by ELISA. Significant low levels of GAS 6 in HCV/T2DM group versus HCV group were detected (7.92 ± 5.18 vs. 16.09 ± 7.36, respectively, p = 0.000), but higher than T2DM and control groups (p ≥ 0.05), although nonsignificant. HCV load was higher in the HCV group than the HCV/T2DM group (1,888,300 ± 5,595,070 vs. 1,417,900 ± 4,066,460 copies/mL, respectively, p = 0.632). Among HCV group, significant positive correlations were detected between Gas6 and sAxl levels with HCV viral load (r = 0.48, p = 0.000 and r = 0.43, p = 0.002, respectively), while among HCV/T2DM group, significant negative correlations were detected (r = −0.29, p = 0.04 and r = −0.34, p = 0.014, respectively). Significant negative correlations were detected between Gas6/sAxl levels and glycated hemoglobin (r = −0.36, p = 0.01 and r = −0.4, p = 0.003, respectively) in T2DM despite the positive correlations detected in HCV/T2DM (r = 0.27, p = 0.053 and r = 0.55, p = 0.000, respectively). In conclusion, Gas6/Axl system in combined HCV/T2DM diseases may affect the pathogenesis and can alter the biomarkers and complications of both diseases in a manner that differs from a solitary disease.

Introduction

Hepatitis C virus (HCV) and type 2 diabetes mellitus (T2DM) are two major public health problems with many complications (9). It was reported previously a correlation between both diseases, although the mechanism is still unclear, it may be due to the abnormal liver condition (16,34). The prevalence of T2DM in HCV-infected patients ranged from 2% to 33% among different countries, which is higher than those reported with other etiologies of chronic hepatitis (1,16,28).

HCV infection is a frequent cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma (HCC) and affects about 170 million individuals worldwide (14). A very high prevalence was reported in Africa (5.3%), with the highest prevalence reported in Egypt (17.5%) (23,25).

Growth arrest-specific protein 6 (Gas6) is the last addition to the family of plasma vitamin K-dependent proteins. It is similar to plasma anticoagulant protein S. It was recognized as a growth factor-like molecule as it interacted with receptor tyrosine kinases of the TAM (Tyro-3, Axl, and Mer) family (4). TAM receptors are postulated to have a role in Flavivirus cell entry (22). Different cell types express Gas6, including leukocytes, platelets, endothelial cells, and vascular smooth muscle (24). The Gas6/Axl system leads to cell survival, proliferation, and cell protection from apoptosis (15). TAM ligands and receptors are also implicated in the regulation of the innate immune response through control of cytokine signaling cascades following tissue injury. Proinflammatory cytokine production by dendritic cells after toll-like receptor activation is attenuated by TAM receptor signaling. Without the TAM receptors, unregulated immunity, autoimmunity, and inflammation will develop (6,24). Soluble forms of Axl and its ligand Gas6 are present in plasma at low concentrations, but usually increased in response to acute phase reactions (6).

In liver pathology, a hepatic protective role of Gas6 has been seen in the healing of wounds (27). In response to liver injury, monocytes migrate from circulation across the endothelium into tissue, promoted by Gas6. Gas6 reduces the secretion of tumor necrosis factor (TNF) and interleukin (IL)-1β in macrophages, liver progenitor cells express Axl and Gas6, which is a survival factor for liver progenitor cells. So Gas6 could protect hepatocytes from cell death (29). Shedding of Axl's ectodomain results in the release of soluble Axl (sAxl), which is increased in all stages of HCC in the presence and absence of cirrhosis (18).

The prevalence of T2DM in Egypt is about 15.6% of all adults aged 20–79 years (17). In T2DM patients, chronic inflammation and activation of the innate immune system are involved in the pathogenesis of this disease. Gas6/TAM signaling resulted in inhibition of the inflammatory response, so the inflammatory effects of high glucose may be through low Gas6 levels in plasma (21). Hung et al. (19) hypothesized that hyperglycemia can cause endothelial dysfunction with downregulation of Gas6/TAM signaling. Furthermore, higher plasma Gas6 concentrations were significantly associated with a decreased risk of T2DM, so elevated plasma Gas6/Axl may be considered protective. In HCV as well as in T2DM, the role of Gas6/Axl system was documented in inflammatory response and pathogenesis of both HCV and T2DM as a solitary disease (6,18,19,21,24,27,29). However, the possible involvement of this system has not been previously addressed in patients affected with both diseases yet, The present study aimed to investigate plasma Gas6 and sAxl levels in HCV patients with and without T2DM compared with healthy control individuals and investigate the association between plasma levels of Gas6/Axl and laboratory markers of HCV infection and T2DM.

Subjects and Methods

A total of 150 adults were recruited from Tropical medicine and Diabetic care out-patient clinics of Fayoum University Teaching Hospital, Egypt, from April 2017 to December 2018. Patients who were eligible to be included in the study were those with HCV infection or with T2DM or those suffering from both diseases.

The exclusion criteria were patients with HCC, rheumatoid diseases, patients with impaired renal function, patients with history of cerebrovascular diseases, myocardial infarction, or heart failure, and patients with autoimmune disorders.

All patients were subjected to clinical assessment in the form of full medical history, clinical examination, abdominal ultrasonography, and laboratory assessment, including liver function tests, complete blood count, international normalized ratio (INR), thyroid-stimulating hormone (TSH), serum creatinine level, random blood sugar (RBS), alpha-fetoprotein, and rheumatoid factor.

Diagnosis of T2DM

T2DM was diagnosed according to the American Diabetes Association criteria (3) when one or more of the following were present: fasting blood glucose ≥126 mg/dL, 2-h postprandial blood glucose test (2hpp) ≥200 mg/dL, glycated hemoglobin (HbA1c) above 6.5%, and RBS value ≥200 mg/dL in presence of symptoms.

Laboratory diagnosis of HCV infection

Detection of HCV antibodies in patient serum was performed by third-generation enzyme-linked immunosorbent assays (ELISA) according to manufacturer's instructions (Abbott-Murex Biotech, Dartford, United Kingdom). Positive cases of HCV by ELISA fulfilled the criteria of the study and were confirmed by real-time RT-polymerase chain reaction (PCR) (DNA-Technology, Russia); after RNA extraction using the QIAmp Viral RNA Kit (QIAGEN, Santa Clarita, CA). The program of real-time PCR (DT-Lite real-time PCR) was adjusted according to the manufacturer's instructions.

According to the result of previous investigations, the patients were classified into three groups with a fourth group, age- and sex matched, included as control; 50 patients with chronic infection of HCV without T2DM, 50 patients with T2DM without HCV infection, 50 patients with chronic HCV and T2DM, and 31 healthy volunteers (negative for HCV antibodies by ELISA and had normal blood glucose level).

Assessment of plasma Gas6 and sAxl

All subjects of the tested groups were tested for Gas6 and sAxl levels in plasma using sandwich technique ELISA kits according to manufacturer's instructions (Bioneovan, Keyuan Road, DaXing Industry Zone, Beijing, China).

The study was approved by Fayoum University Research Ethical Committee and conforms to the provisions of the Declaration of Helsinki in 1995. All subjects gave their informed consent before their inclusion in this study.

Statistical analysis

Data were collected and coded, then analysis was performed using SPSS (Statistical package for the social sciences) software version 22 (SPSS, Inc.). For quantitative data, one way ANOVA test was used as a test of significance to compare means. Multiple comparisons between pairs of groups were performed using Least Significant Difference (LSD) post hoc test. Pearson correlation was run to identify correlation of Gas6 and sAxl levels with study parameters in different study groups. Qualitative data were presented as number and percentages; chi square (χ ²) or Fisher's exact test, when appropriate, was used as a test of significance. p Value ≤0.05 was considered significant and p value ≤0.001 was considered highly significant.

Results

Regarding HCV-infected groups with and without T2DM, our results revealed that alanine aminotransferase (ALT), aspartate aminotransferase (AST), INR, and total bilirubin are significantly higher than T2DM and control groups (p ≤ 0.002). On the contrary, platelet counts and albumin are significantly lower than T2DM and control groups (p < 0.05) (Table 1).

Table 1.

Anthropometric and Biochemical Variables Among Study Groups

Variables	HCV (n = 50), mean ± SD	HCV/T2DM (n = 50), mean ± SD	T2DM (n = 50), mean ± SD	Control (n = 31),mean ± SD	p
Sex (male:female ratio)	18:32	10:40	24:26	14:17	≤0.016^d,e
Sex (male:female ratio)	18:32	10:40	24:26	14:17	>0.05^a,b,c,f
Age (years)	53.2 ± 12.16	57.7 ± 8.34	53.12 ± 10.71	50.25 ± 6.85	0.00^e
					<0.05^a,d
					>0.05^b,c,f
Weight (kg)	77.56 ± 12.40	73.4 ± 10.83	80.48 ± 11.29	81.64 ± 16.33	<0.05^d,e
Weight (kg)	77.56 ± 12.40	73.4 ± 10.83	80.48 ± 11.29	81.64 ± 16.33	>0.05^a,b,c,f
Height (cm)	160.44 ± 8.4	158.76 ± 8.59	159.76 ± 9.25	163.81 ± 9.061	<0.05^e,f
Height (cm)	160.44 ± 8.4	158.76 ± 8.59	159.76 ± 9.25	163.81 ± 9.061	>0.05^a,b,c,d
BMI (kg/m²)	29.95 ± 4.05	28.9 ± 4.57	31.75 ± 5.46	30.41 ± 5.61	<0.05^b,d
BMI (kg/m²)	29.95 ± 4.05	28.9 ± 4.57	31.75 ± 5.46	30.41 ± 5.61	>0.05^a,c,e,f
Hemoglobin (g/L)	12.68 ± 1.59	12.59 ± 1.39	12.69 ± 1.24	11.78 ± 1.26	<0.05^c,e,f
Hemoglobin (g/L)	12.68 ± 1.59	12.59 ± 1.39	12.69 ± 1.24	11.78 ± 1.26	>0.05^a,b,d
Platelet count/μL	118,440 ± 48672.23	110,720 ± 42110.17	266,880 ± 48304.57	263,070 ± 48199.96	0.000^b,c,d,e
Platelet count/μL	118,440 ± 48672.23	110,720 ± 42110.17	266,880 ± 48304.57	263,070 ± 48199.96	>0.05^a,f
Serum ALT (U/L)	47.4 ± 45.51	49.66 ± 46.8	17.04 ± 9.52	12.8 ± 6.78	0.000 ^b,c,d,e
Serum ALT (U/L)	47.4 ± 45.51	49.66 ± 46.8	17.04 ± 9.52	12.8 ± 6.78	>0.05^a,f
Serum AST (U/L)	51.12 ± 45.89	48.42 ± 33.68	14.7 ± 8.88	10.48 ± 5.04	0.000^b,c,d,e
Serum AST (U/L)	51.12 ± 45.89	48.42 ± 33.68	14.7 ± 8.88	10.48 ± 5.04	>0.05^a,f
Serum albumin (g/L)	3.65 ± 0.52	3.86 ± 0..49	4.19 ± 0.64	4.22 ± 0.33	<0.05^a,d,e
					0.000^b,c
					0.8^f
Total bilirubin (mg/dL)	0.89 ± 0.38	0.92 ± 0.40	0.66 ± 0.21	0.43 ± 0.17	≤0.002^b,c,d,e,f
Total bilirubin (mg/dL)	0.89 ± 0.38	0.92 ± 0.40	0.66 ± 0.21	0.43 ± 0.17	0.623^a
RBS	109.04 ± 18.03	222.36 ± 57.58	280.36 ± 49.54	103.68 ± 15.85	0.000^a,b,d,e,f
RBS	109.04 ± 18.03	222.36 ± 57.58	280.36 ± 49.54	103.68 ± 15.85	0.574^c
FBG (mmol/L)	NM	155.60 ± 51.28	154.04 ± 22	NM	0.844^d
2hpp (mmol/L)	NM	233.68 ± 60.09	260 ± 40.43	NM	0.012^d
HbA1c (%)	NM	7.23 ± 0.46	8.05 ± 1.25	−NM	0.000^d
INR	1.11 ± 0.12	1.12 ± 0.11	1 ± 0	1 ± 0	0.000^b,c,d,e
					0.586^a
					1^f
Serum creatinine (mg/dL)	0.75 ± 0.17	0.72 ± 0.16	0.77 ± 0.23	0.71 ± 0.11	>0.05^a,b,c,d,e,f
TSH (mU/L)	2.15 ± 3.01	1.85 ± 2.58	1.62 ± 0.8	1.13 ± 0.36	0.041^c
TSH (mU/L)	2.15 ± 3.01	1.85 ± 2.58	1.62 ± 0.8	1.13 ± 0.36	>0.05^a,b,d,e,f
HCV viral load (copies/mL)	1,888,300 ± 5,595,070	1,417,900 ± 4,066,460	NM	NM	0.632^a

Bold values are significant at p < 0.05.

Significance between HCV and (HCV + DM).

Significance between HCV and DM.

Significance between HCV and control.

Significance between (HCV + DM) and DM.

Significance between (HCV + DM) and controls

Significance between DM and control.

2hpp, 2 h postprandial; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BMI, body mass index; DM, diabetes mellitus; FBG, fasting blood glucose; HbA1c, glycated hemoglobin; HCV, hepatitis C virus; INR, International normalized ratio; NM, not measured; RBS, random blood sugar; SD, standard deviation; T2DM, type 2 diabetes mellitus; TSH, thyroid stimulating hormone.

TSH is significantly higher in HCV group than control group (p = 0.041) (Table 1).

When comparing RBS levels in different study groups, we found highly significant low levels in HCV/T2DM group than T2DM group (p = 0.000), also 2hpp and HbA1c levels are significantly lower in HCV/T2DM group versus T2DM group (p ≤ 0.012) (Table 1).

Our results revealed that plasma levels of Gas6 as well as sAxl were significantly higher in HCV group than all other tested groups (p = 0.000). Also plasma levels of Gas6 were significantly higher in HCV/T2DM group versus T2DM and control groups (p < 0.05) (Table 2).

Table 2.

Gas6 and sAxl Plasma Levels in Different Study Groups

Study groups	Gas6 concentrations (ng/mL)		sAxl concentrations (ng/mL)
Study groups	Mean ± SD	p	Mean ± SD	p
HCV	16.09 ± 7.36	0.000^a,b,c,e 0.022^d 0.1^f	11.92 ± 3.12	0.000 ^a,b,c 0.35^d 0.25^e 0.73^f
HCV + T2DM	7.92 ± 5.18		7.01 ± 1.79
T2DM	5.21 ± 6.16		7.75 ± 5.73
Control	2. 99 ± 3.06		8.06 ± 4.30

Bold values are significant at p < 0.05.

Significance between HCV and (HCV + DM).

Significance between HCV and DM.

Significance between HCV and control.

Significance between (HCV + DM) and DM.

Significance between (HCV + DM) and controls.

Significance between DM and control.

Plasma Gas6 levels showed significantly positive correlation with sAxl levels among all tested groups except the healthy control group (p ≤ 0.021) (Table 3).

Table 3.

Correlation Between Plasma Levels of Gas6 and sAxl with Different Variables Among Study Groups

Variables	HCV				T2DM				HCV and T2DM				Control
	Gas6		sAxl		Gas6		sAxl		Gas6		sAxl		Gas6		sAxl
	r	p	R	p	r	p	r	p	r	p	r	p	r	p	r	p
Age (years)	0.34 ^*	0.016	−0.008	0.95	0.3 ^*	0.03	0.39 ^**	0.004	−0.03	0.8	0.08	0.55	−0.37 ^*	0.03	0.10	0.58
Weight	0.43 ^**	0.001	−0.02	0.85	−0.004	0.97	−0.16	0.25	0.001	0.99	0.13	0.33	0.002	0.99	0.1	0.56
Height	0.20	0.16	0.21	0.14	−0.01	0.9	−0.08	0.55	0.11	0.41	0.26	0.06	0.31	0.08	−0.22	0.22
BMI	0.36 ^**	0.01	−0.2	0.14	−0.05	0.68	−0.19	0.17	−0.08	0.57	−0.06	0.64	−0.18	0.33	0.26	0.15
Hemoglobin	−0.12	0.39	0.06	0.66	0.23	0.09	0.35 ^*	0.013	−0.33 ^*	0.019	−0.37 ^*	0.008	−0.14	0.4	0.45 ^*	0.01
platelets count	−0.09	0.51	−0.12	0.57	0.19	0.17	0.2	0.14	0.23	0.09	−0.04	0.76	−0.27	0.13	0.31	0.08
ALT	−0.05	0.722	−0.03	0.61	0.015	0.92	−0.09	0.51	0.14	0.31	−0.29 ^*	0.04	−0.27	0.13	−0.10	0.56
AST	0.002	0.988	−0.01	0.89	−0.19	0.18	−0.21	0.13	−0.07	0.63	−0.11	0.41	0.18	0.31	0.03	0.8
Albumin	−0.13	0.35	−0.12	0.4	0.21	0.13	−0.05	0.72	0.08	0.56	0.11	0.42	0.01	0.95	0.29	0.1
Total bilirubin	0.196	0.17	0.019	0.89	−0.23	0.1	−0.13	0.34	−0.22	0.11	−0.01	0.9	−0.27	0.13	0.25	0.17
RBS	−0.03	0.8	0.27	0.057	0.039	0.78	0.25	0.08	−0.30 ^*	0.03	−0.21	0.13	0.03	0.8	0.2	0.26
FBG	—	—	—	—	−0.17	0.22	−0.18	0.2	0.11	0.42	0.02	0.89	—	—	—	—
2hpp	—	—	—	—	0.08	0.56	0.19	0.17	0.04	0.75	−0.12	0.37	—	—	—	—
HbA1c	—	—	—	—	−0.36 ^*	0.01	−0.4 ^*	0.003	0.27	0.053	0.55 ^**	0.000	—	—	—	—
INR	0.35 ^*	0.011	0.16	0.26	—	—	—	—	−0.03	0.8	0.12	0.6	—	—	—	—
Creatinine	−0.002	0.98	−0.47 ^**	0.001	−0.25	0.07	−0.25	0.072	0.22	0.12	0.08	0.57	−0.15	0.4	0.27	0.13
TSH	−0.205	0.396	0.05	0.68	0.36 ^*	0.009	0.34 ^*	0.014	0.01	0.9	−0.05	0.68	−0.26	0.16	0.29	0.10
HCV viral load	0.48 ^**	0.000	0.43 ^*	0.002	—	—	—	—	−0.29 ^*	0.04	−0.34 ^*	0.014	—	—	—	—
sAxl concentration	0.32 ^*	0.021	—	—	0.82 ^**	0.000	—	—	0.69 ^**	<0.000	—	—	−0.31	0.06	—	—

Bold values are significant at p < 0.05.

^{^*}Significant.

^{^**}Highly significant.

As shown in Table 3, among HCV group, significant positive correlations were detected between Gas6 levels with age, weight, body mass index (BMI), INR, and HCV viral loads (p ≤ 0.016), while sAxl levels were significantly positively correlated with serum creatinine and HCV viral loads (p ≤ 0.002). Unexpectedly, significant negative correlations were detected between both Gas6 and sAxl levels with HCV viral load among HCV/T2DM group (p ≤ 0.04). Significant negative correlations were detected between Gas6 and sAxl levels and HbA1c (p ≤ 0.01) in T2DM despite positive correlations of Gas6 and sAxl levels detected in HCV/T2DM (r = 0.27, p = 0.053 and r = 0.55, p = 0.000, respectively). Significant negative correlations were detected between both Gas6 and sAxl levels with hemoglobin concentrations in HCV/T2DM group (p ≤ 0.019).

Among diabetes mellitus (DM) group, both Gas6 and sAxl levels showed significant positive correlations with age and TSH levels (p ≤ 0.014).

Discussion

HCV has been identified as a leading cause of chronic liver disease with sever sequel. Several studies had implicated the HCV infection in the development of diabetes, while others reported T2DM as a predisposing risk factor for HCV infection. The prevalence of T2DM in HCV-infected patients ranged from 2% to 33% among different countries, which is higher than those reported with other etiologies of chronic hepatitis (1,16,28). Elevated liver enzymes are generally acknowledged as an important marker for liver injury (11). Our results revealed that in HCV-infected groups (with and without T2DM), ALT and AST are significantly higher than those reported in T2DM and control groups (p = 0.000). These results indicated liver damage with subsequent poor liver functions as recorded by significant low platelet count and serum albumin versus those of T2DM and control groups (p < 0.05) and significant higher INR and total bilirubin levels than those reported in T2DM and control groups (p = 0.002).

The present results revealed that TSH is significantly higher in the HCV group than the control group (p = 0.041). Thyroid involvement is a frequent endocrine disorder usually reported in association with HCV infection, and HCV patients are more likely to develop hypothyroidism as an extrahepatic autoimmune disease (10). This can explain our result although we miss the high significant levels in the HCV/T2DM group. A possible explanation is the association of both hypothyroidism and hyperthyroidism with T2DM, which was linked to insulin resistance (IR) and subsequent impaired glucose metabolism in T2DM (36).

The present results revealed that BMI is significantly lower in HCV and HCV/T2DM groups versus T2DM group (29.95 ± 4.05 and 28.9 ± 4.57 kg/m² vs. 31.75 ± 5.46 kg/m², respectively, p < 0.05). Previous studies had reported that obesity is among the most important risk factors for T2DM; Ghouri et al. (12) found that only 25% of diabetic patients had BMI less than 25 kg/m². Narita et al. (30) and Wang et al. (35) reported that increase in BMI >25 kg/m² was associated with increased risk of DM in patients with HCV infection without a family history of DM.

The marked inflammatory response to HCV is central to the development of hepatic and peripheral IR in chronic HCV infection, mainly through disruptions of the insulin signaling pathway. Previous studies had reported that TNF alpha (TNF-α) directly interferes with insulin signaling in HCV patients (7,16). Also, Knobler et al. (20) reported a significantly more detectable serum TNF-α in diabetic HCV-infected patients than in control group (p < 0.0001). Unexpectedly, the present results detected significant lower levels of RBS, 2hpp, and HbA1c in HCV/T2DM group versus T2DM group (p ≤ 0.012). Yet, this can be explained by the significant higher levels of GAS6 in HCV/T2DM group versus T2DM group (7.92 ± 5.18 vs. 5.21 ± 6.16, respectively, p = 0.022). GAS6 was reported to have an inhibitory role on TNF-α, IL-1, and IL-6 expression (2,13).

The present results revealed that plasma levels of Gas6, as well as sAxl, were significantly higher in the HCV group than all other tested groups (p = 0.000), also Gas6 levels were significantly higher in the HCV/T2DM group than those of T2DM and control groups (p ≤ 0.022) (Table 2). Gas6 and sAxl levels were reported to be increased in parallel to chronic liver disease progression (5,18). So the present results could be accepted.

The present work detects significant negative correlations between Gas6 and sAxl levels and HbA1c (p ≤ 0.01) in T2DM despite positive correlation detected in the HCV/T2DM group. The previous works are contradictory; Erek-Toprak et al. (8) reported positive correlation between Gas6 and HbA1c in T2MD (ρ = 0.331, p = 0.01), while Lee et al. (26) reported negative correlation between Gas6 and HbA1c in patients who had undergone coronary artery bypass grafting as well as healthy controls in whom diabetic patients represent 63% and 60%, respectively (r = −0.305, p = 0.18 and r = −0.521, p = 0.004, respectively).

The present results revealed that Gas6 and sAxl levels were significantly positively correlated with HCV viral load (p ≤ 0.002) in HCV group and HCV load was higher in HCV group than HCV/T2DM group although nonsignificant (1,888,300 ± 5,595,070 copies/mL vs. 1,417,900 ± 4,066,460 copies/mL, respectively, p = 0.632). Chronic HCV patients with prolonged activation of Interferons (type I/III) signaling pathways are less likely to develop sustained virological response to treatment (29). An Axl role has been suggested in vivo and in vitro as an explanation; Axl expression was reported to be upregulated in chronically infected hepatocytes; especially in patients with a “non-responder” phenotype; this may be a direct effect of Axl on IFN signaling pathways (32,33). Noh et al. (31) reported that serum HCV viral load could be considered an independent risk factor for the development of HCC. Furthermore, Holstein et al. (18) linked the increased plasma Gas6 and sAxl levels to HCC carcinoma and suggested that Gas6 and Axl represent an oncogenic driver. In this line, patients in the HCV group are supposed to be at an increased risk to develop HCC. Unexpectedly, significant negative correlations were detected between both Gas6 and sAxl levels with HCV viral load among the HCV/T2DM group (p ≤ 0.04), suggesting an active role of T2DM in the pathogenesis of HCV, which could be mediated through a Gas6/Axl pathway.

To our knowledge, this work is the first one to investigate the plasma levels of Gas6/Axl in the HCV/T2DM group. Our results highlighted some interesting points in this group; first, the significant negative correlations between both Gas6 and sAxl levels and HCV viral load. Second, the significant low levels of GAS6/sAxl in HCV/T2DM group versus HCV group, although both HCV infection and T2DM are characterized by chronic inflammation and elevation of Gas6/sAxl levels (18,21), we were expecting their levels to be higher than HCV group. Third, the significant lower levels of RBS, 2hpp, and HbA1c in HCV/T2DM group versus T2DM group. It seems that the pathogenesis in HCV/T2DM group is multifactorial, but we proposed that Gas6 and Axl are the key players. Further researches are needed to clarify their exact role. The reduced clinical data are among the study limitations and further analyses with respect to patients' disease characteristics, complications, and medications received are recommended.

In conclusion, Gas6/Axl system in combined HCV/T2DM diseases may affect the pathogenesis and can alter the biomarkers and complication of both diseases in a manner that differ from each disease alone. Additional efforts are required to entirely translate how Gas6/Axl pathway may modulate the immune system in HCV/T2DM patients. An interdisciplinary approach will be necessary for better understanding of the pathways, by which Gas6/Axl might influence the pathogenesis in HCV/T2DM patients.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received.

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