As previously mentioned, evidence accumulated over many years indicates that gallstones can induce an inflammatory microenvironment that increases the risk of developing GBC. However, this risk can be fostered by a greater genetic predisposition
[122][53], for example, the genetic variability present in genes that encode the different ATP-binding cassette (ABC) transporters in the hepatocanalicular membrane, which are involved in the different processes of the exportation of bile salts in biliary tracts, including the transportation of ABCB11, the transport of phosphatidylcholine (ABCB4), and secretion of cholesterol and phytosterols into bile (heterodimer ABCG5/8)
[123][54]. In this regard, a genetic variant in the
ABCG8 gene (variant rs11887534 or D19H) has been associated with a higher gallstone development through cholesterol hypersecretion and cholesterol supersaturation in the bile
[122,124][53][55]. In addition, other variants (rs1558375, rs17209837, and rs4148808) have been determined in the 7q21.12 region harboring both the
ABCB1 and
ABCB4 genes, which showed a higher risk of developing GBC
[28][56]. A study by Bustos et al. showed that in the Chilean Mapuche ancestry population, variants in
ABCG8 (rs11887534) and
TRAF3 (rs12882491) were associated with GSD. In addition, it was shown that TRAF3 levels were lower in individuals affected by GSD, suggesting that these variants could be used as risk markers for GBC
[125,126][57][58]. Other mutations occur in the
ABCB4 gene and are classified as nonsense mutations (class I), missense mutations affecting maturation (class II), activity (class III), or protein stability (class IV), and mutations with no identifiable effect (class V)
[127][59]. It has been shown that mutations in this gene increase the risk of developing gallstones in subjects under 40 years, mainly by inducing an
ABCB4 deficiency that results in low biliary phosphatidylcholine concentrations, which is consistent with the spontaneous occurrence of cholecystolithiasis
[128,129][60][61]. In fact, the homozygous
ABCB4 mutations lead to the complete absence of the phospholipid transporter and no secretion of phospholipids into bile, which finally causes a decrease in the solubility of bile, and consequently, a greater predisposition to bile crystallization and gallstone formation
[130][62]. Other mutations and alterations have been described in different genes and proteins potentially involved in a higher risk of developing gallstones, such as ABCB11
[130][62], cholesterol 7a-hydroxylase (CYPA1)
[131[63][64],
132], APOB gene
[133][65], and cholecystokinin A receptor (CCKAR)
[134,135][66][67]. In addition, certain alterations in genes related to the immune system, inflammation, and oxidative stress have also been implicated in a greater risk of developing GBC, including mutations in
TLR2, TLR4 [136][68],
IL1RN, IL1B [137][69],
IL10, IL8, IL8RB, RNASEL, VEGF [138][70], and
CCR5 [139][71], as well as rs7504990 variant in the
DCC [140][72]. These data show that the predisposition to developing cholecystolithiasis and GBC also have an important genetic background that needs to be considered in GBC carcinogenesis.
Finally, another risk factor associated with GBC is the appearance of bluish and brittle calcifications in the inner gallbladder wall named "porcelain gallbladder"
[141][73]. Porcelain gallbladder has an incidence of less than 1% in patients with gallbladder disease, being more prevalent in women
[141][73]. This rare condition is considered a risk factor for GBC because approximately 60% to 90% of these cases show gallstones
[141,142][73][74]. Despite the pathophysiology of "porcelain gallbladder" not being clear, this condition could be a consequence of a previous chronic inflammatory process or could be the result of an obstruction produced by gallstones that induce the accumulation and precipitation of calcium in the mucosal layer of the gallbladder wall
[143][75]. Whatever the origin of this disease, it is also unknown whether calcium levels play a role in the “porcelain gallbladder” pathogenesis. Recently, Berger et al. found significantly higher calcium and parathormone (PTH) levels in the plasma of individuals with porcelain gallbladder compared to controls
[144][76], which suggests that individuals with diseases that induce persistent hypercalcemia (e.g., primary hyperparathyroidism) also have a higher risk of developing porcelain gallbladder. In this regard,
wthe researche
rs venture to propose that persistent hypercalcemia could be an initiating factor of porcelain gallbladder, which would eventually trigger the formation of a chronic inflammatory state in the inner layer of the gallbladder, increasing in this manner the risk of developing GBC. However, more studies are still needed to demonstrate this hypothesis.
FigureFigure 2 3 shows the relationship between the risk factors described above and their involvement in GBC inflammation and carcinogenesis.
Figure 3Figure 2. Carcinogenesis process in gallbladder cancer. The damage caused by the presence of risk factors such as gallstones, infections, lithogenic bile, alcohol, smoking, and genetic predisposition can induce continuous damage in the mucosa of the gallbladder, which is characterized by a chronic inflammatory state mainly highlighted by the activation of macrophages and lymphocytes that leads to the release of pro-inflammatory cytokines (TNF-α, IL-6, IL-1) and ROS stimulating the carcinogenic metaplasia/hyperplasia–dysplasia–carcinoma transition. This process can be marked by different gene alterations and protein expressions such asTP53andFHITmutations and COX-2, TNF-α, and CLDN-18 overexpression, respectively. BMI: Body Mass Index; TNF-α: Tumor necrosis factor-alpha; ROS: Reactive oxygen species; IL-1: Interleukin-1; IL-6; Interleukin-6; CLDN-18: Claudin18; COX-2: Cyclooxygenase 2; TP53: Tumor protein 53; FHIT: Fragile Histidine Triad Diadenosine Triphosphatase. The risk factors in bold mean strong evidence. The risk factor in italics and underlined means weak evidence