Long-term safety and efficacy of alirocumab in patients with heterozygous familial hypercholesterolemia: An open-label extension of the ODYSSEY program

Figure 1. Lack of LDL receptor-induced hypercholesterolemia causes LDL cholesterol to rise. This in turn results in accumulation of fat under the skin in various parts of the body seen as xanthoma. Fat accumulation also occurs in the arteries and blockage of coronary artery leads to heart attack and blockage of carotid and other arteries causes stroke.

Figure 2. Mechanism of siRNA-mediated gene silencing. Small interfering RNAs (siRNAs) mediate sequence-specific post-transcriptional gene silencing through the endogenous RNA interference (RNAi) pathway. Following delivery into target cells, siRNAs are released into the cytoplasm and incorporated into the RNA-induced silencing complex (RISC). The passenger strand is degraded, while the guide strand directs RISC to complementary target mRNA sequences. Argonaute-mediated cleavage of the target mRNA triggers its degradation, preventing translation and reducing synthesis of the encoded protein. Through catalytic turnover, a single siRNA-loaded RISC can silence multiple mRNA molecules, resulting in potent and highly specific gene knockdown.

Figure 3. Panel 1. miRNA Biogenesis in the Nucleus. miRNA genes are transcribed by RNA polymerase II to generate primary miRNA transcripts (pri-miRNAs). The Drosha–DGCR8 microprocessor complex cleaves pri-miRNAs into precursor miRNAs (pre-miRNAs), which are subsequently exported to the cytoplasm by Exportin-5. Panel 2. Cytoplasmic Processing of pre-miRNAs. In the cytoplasm, Dicer cleaves pre-miRNAs to generate a mature miRNA duplex. The passenger strand is degraded, while the guide strand is retained for incorporation into the RNA-induced silencing complex (RISC). Panel 3. RISC Assembly. The guide miRNA strand is loaded onto an Argonaute-containing RISC, forming the active silencing machinery responsible for recognizing and regulating target mRNAs. Panel 4. Target Recognition and Gene Silencing. The miRNA-RISC complex binds complementary sequences, typically within the 3′ untranslated region (3′UTR) of target mRNAs. This interaction promotes translational repression, mRNA deadenylation, destabilization, and degradation, resulting in reduced protein expression.

Figure 4. Schematic illustration highlighting the advantages of miR-30c-mediated MTTP inhibition over currently marketed therapies targeting MTTP activity or apoB synthesis. Hepatic assembly and secretion of apoB-containing lipoproteins (VLDL) require two essential components: apolipoprotein B (apoB) and MTTP. Inhibition of MTTP by the small-molecule inhibitor lomitapide (Juxtapid®) or suppression of apoB synthesis by the antisense oligonucleotide mipomersen (Kynamro®) impairs VLDL assembly and secretion, thereby reducing circulating LDL-C levels. However, because hepatic fatty acid synthesis continues despite impaired lipoprotein export, triglycerides accumulate within hepatocytes, leading to hepatic steatosis (fatty liver) accompanied by elevated plasma AST and ALT levels, reflecting liver injury. In contrast, although miR-30c inhibits MTTP and reduces apoB-containing lipoprotein secretion, it simultaneously suppresses hepatic fatty acid synthesis pathways, including targets such as LPGAT, thereby maintaining hepatic lipid homeostasis. As a result, no significant hepatic fat accumulation or elevations in AST and ALT have been observed in multiple preclinical models treated with miR-30c…

Figure 5. Complementary miRNA control nodes in cholesterol metabolism: miR-148a versus miR-30c. Schematic comparison of LDLR-dependent and LDLR-independent miRNA pathways regulating plasma LDL-C. (Left): miR-148a represses LDL receptor (LDLR) expression via binding to the LDLR 3′UTR, reducing hepatic LDL uptake. Relief from miRNA-mediated repression—illustrated by antisense inhibition or the Icelandic LDLR 3′UTR del2.5 variant—enhances LDLR abundance and promotes LDL clearance, primarily benefiting polygenic hypercholesterolemia. (Right): miR-30c acts independently of LDLR by repressing microsomal triglyceride transfer protein (MTTP), thereby reducing apoB lipidation and VLDL assembly. Concurrent suppression of de novo lipogenesis by inhibiting fatty acid synthesis and enhancement of fatty-acid oxidation preserves hepatic lipid balance, relevant for LDLR-independent pathway. Together, these pathways illustrate how miRNAs function as network calibrators to achieve durable cholesterol lowering through complementary mechanisms.

Figure 6. miRNA30c coordinately inhibits lipoprotein secretion via MTTP suppression and reduced hepatic lipid synthesis via inhibition of LPGAT and other fatty acid synthesis enzymes. In addition, miRNA30c also enhances fatty acid oxidation and degradation which contributes to the reduction in the hepatic lipid content. Together, these coordinated actions of miR30c in the liver leads to potent reduction of atherogenic lipoproteins in the blood without hepatic fat accumulation.

Figure 7. Mode of action of miR-30c analog C2 in inhibiting progression of atherosclerotic plaque. miR-30c analog C2 maintains hepatic lipid homeostasis through a coordinated multi-target mechanism. Its primary action involves downregulation of microsomal triglyceride transfer protein (MTTP), resulting in reduced assembly and secretion of apoB-containing lipoproteins. Simultaneously, miR-30c analog C2 suppresses hepatic fatty acid synthesis through inhibition of lipogenic pathways, including downregulation of LPGAT1. In addition, RNA-seq analyses (216) demonstrated upregulation of genes involved in fatty acid oxidation and lipid degradation. Together, these integrated actions reduce substrate availability for VLDL production while preventing hepatic lipid accumulation. These effects were consistently observed in both mouse models and non-human primates. Beyond its effects on hepatic lipoprotein metabolism, miR-30c analog C2 also enhances whole-body cholesterol elimination by inducing the cholesterol transporters ABCG5 and ABCG8, thereby increasing fecal sterol excretion in both rodents and non-human primates. Collectively, these mechanisms lead to marked anti-atherosclerotic effects,…